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2021 GMC Sierra HD Review

The 2021 GMC Sierra HD is an impressive pickup truck with far-reaching abilities. Along with its mechanical partner, the Chevrolet Silverado HD, the Sierra HD is in the second year of a new generation. Where GMC differs from Chevy is that it’s usually a little more upscale. But this is an excellent truck no matter what badge it’s wearing.

Heavy-duty trucks, known technically as Class 2B and Class 3, are tools for hard work, specifically towing and hauling. The 2500HD version has a maximum payload rating of 3,863 pounds and can tow 18,500 pounds. The 3500HD can carry 6,610 pounds and pull 20,000 pounds with a conventional trailer, or 36,000 pounds with dual rear wheels, gooseneck/fifth-wheel connection, and the optional high-torque diesel engine.

These aren’t class-leading numbers, but they’re still impressive and probably good enough for most buyers’ requirements. And there are many tech features devoted to eliminating stress from the tricky art of towing.

It’s not all about work, though. The 2021 Sierra HD range also has spacious and hushed cabins, an off-roading AT4 model, and a luxurious Denali version.

What’s New for 2021?

Despite being so new, the Sierra HD has received several updates for this model year. Wireless Apple CarPlay/Android Auto smartphone integration becomes standard at the SLT trim level. The MultiPro 6-function tailgate is now standard in the SLE trim and above. The range-topping Denali trim receives bed-view and trailer-view cameras, plus a 360-degree high-definition camera system as standard.

Maximum towing capacity has been raised to 36,000 pounds (in a properly equipped 3500HD).

Optional equipment also sees a shake-up, especially in the towing department. A jack-knife alert is introduced. A new trailer length indicator shows an image on the center screen of any vehicles within the vicinity of the trailer that might interfere with a change of lanes.

The rear trailer view feature now includes guidelines and a trailer angle indicator. Rear Side View is enhanced, providing a split left/right image of the trailer when reversing. And a new cargo bed zoom view with bed hitch guidance is now available, making it easier to align with and connect a gooseneck/fifth-trailer.

The SLT Premium package gains chromed steps and a spray-in bed liner. The AT4 Premium Plus package adds both Driver Alert arrays, 20-inch alloy wheels, and a high-clearance step.

The X31 Off-road suspension/protection package for SLE and SLT trims brings a lot of the all-terrain hardware of the specialist AT4 variant. Speaking of the AT4, it’s now offered with 20-inch Goodyear Wrangler Territory tires.

A new Black Diamond Edition for the Denali trim includes an auxiliary trailer camera, trailer tire pressure monitoring, power-retractable steps with LED perimeter lighting, 20-inch alloy wheels finished in high-gloss black, and a Kicker audio system. See the 2021 GMC Sierra 2500HD models for sale near you or see the 2021 GMC Sierra 3500HD models for sale near you

What We Like

What We Don’t

  • Interior design not as agreeable as some rivals
  • The push toward premium comes with high prices

How Much?

$37,495 – $67,695

Fuel Economy

The Sierra HD comes with a naturally aspirated (no turbocharger or supercharger) 6.6-liter V8 engine with direct gasoline injection. It produces 401 horsepower and 464 lb-ft of torque, and a 6-speed automatic transmission sends that to the rear wheels in the truck’s basic form. All-wheel drive (with a 2-speed transfer case) is also available. It’s optional in the first three trim levels and standard in the AT4 and Denali models. 

A Duramax 6.6-liter V8 turbodiesel engine is available as an option (the best part of $10,000). It uses common-rail direct fuel injection to develop 445 hp and an immense 910 lb-ft of torque. This unit pairs with a 10-speed automatic transmission from Allison, a highly respected third-party manufacturer/supplier.

Sierra HD models have gross vehicle weight ratings (GVWR) of over 8,500 pounds and are not subject to fuel economy tests or ratings by the Environmental Protection Agency (EPA).

Standard Features and Options

The 2021 GMC Sierra HD comes as a 2500HD or 3500HD model, and in base, SLE, SLT, AT4, and Denali trim levels. Cab configurations are regular, Double, or Crew. Where it isn’t standard, all-wheel drive costs $2,800.

The standard bed length measures 6.8 feet. For an additional $200, a long bed (8.2 feet) is also available. Both sizes include cargo-bed-side steps, integrated CornerSteps in the rear bumper, cargo area lighting, and 12 fixed tie-down points.

The regular cab comes solely with a long bed. In 2500HD form, the Double cab can be paired with either bed, but the 3500HD version comes only with the long bed. Every Crew cab offers the choice of beds. Single rear wheels are standard across the range; dual rear wheels are available on the 3500 models.

The base Sierra HD ($37,495: 2500HD, $37,795: 3500HD) has 17-inch steel wheels, LED headlights/daytime running lights/taillights, a rearview camera, manual locks/windows, vinyl flooring, manually adjustable front seats, height-adjustable plastic steering wheel, single-zone air conditioning, programmable Teen Driver key, 7-inch infotainment touch screen, two USB ports, Apple CarPlay/Android Auto smartphone integration, Bluetooth, AM/FM radio, and either a 2-speaker audio setup in the regular cab or a 6-speaker system in the Double and Crew cabs. These two bigger cabs also have a Rear Seat Reminder.

This base model isn’t eligible for many options but can be ordered with heated/power-adjustable side mirrors, MultiPro 6-function tailgate, forward collision alert, automatic emergency braking, blind-spot monitoring with rear cross-traffic alert, power locks, power windows, and a spray-in bed liner.

SLE ($42,595: 2500HD, $43,795: 3500HD) has 17-inch alloy wheels, MultiPro 6-function tailgate, carpeted flooring, power-adjustable side mirrors, cruise control, leather-wrapped steering wheel, Wi-Fi, and GM’s OnStar service.

An SLE Convenience package brings most of the extra features that the next-up SLT trim has as standard.

SLT ($52,595: 2500HD, $55,595: 3500HD) starts off with the Double cab and standard bed, adding variable steering assistance, ProGrade Trailering system, Hitch Guidance with Hitch View, In-Vehicle Trailering app, keyless entry/ignition, remote start, heated/self-dimming side mirrors, LED fog lights, perimeter lighting, a high-definition rearview camera, heated/10-way power-adjustable front seats with driver’s-side memory settings, heated steering wheel (that also adjusts for reach), dual-zone automatic climate control, self-dimming rearview mirror, rear under-seat storage, 12-volt outlet, 110-volt outlet, wireless Apple CarPlay/Android Auto, two more USB ports for rear passengers, and SiriusXM 360L satellite radio.

A new-for-2021 SLT Premium options package contains heated/ventilated front bucket seats, heated rear seats, powered rear sliding window, universal garage door opener, spray-in bed liner, bed-view/trailer-view cameras, 360-degree high-definition camera system, Driver Alert Package I (see the Safety section below), 8-inch infotainment touchscreen, wireless charging, and a 7-speaker Bose audio system. These features can be split up into smaller bundles.

Both the SLE and SLT trims are offered with an X31 Off-Road and Protection package (not available with dual rear wheels) that includes specialist Rancho twin-tube shock absorbers, skid plates for the transfer case and oil pan, all-weather floor liners, spray-in bed liner, and hill descent control. Cab-length chrome assist steps are also available in the SLE and SLT.

The AT4 ($59,995: 2500HD, $61,195: 3500HD) comes as a Crew cab and with all-wheel drive as standard. It has the contents of the X31 package above, plus other specific enhancements such as an Eaton locking rear differential, 18-in wheels (with 20-in wheels available), all-terrain tires, hill descent control/hill start assistance, and a traction control system with an off-road mode.

The AT4’s interior receives a darkened trim on the steering wheel, center stack and sill plates, heated/ventilated front bucket seats. Heated outboard rear seats, center console, Jet Black leather upholstery with Kalahari tan accents, plus embroidered AT4 logos on the headrests and all-weather floor liners.

The exterior has a textured grille in black chrome, dark chrome exterior details, body-colored bumpers, red recovery hooks, AT4 badging, and a spray-in bed liner.

An optional AT4 Premium Plus Package is also new for 2021. It includes both Driver Alert packages (see the Safety section below), Rear Camera Mirror, 15-in head-up display with an off-road Inclinometer, bed-view/trailer-view cameras, universal garage door opener, wireless charging, 8-inch infotainment touchscreen, navigation, 7-speaker Bose audio system, and a 360-degree high-definition camera system for studying the surrounding terrain at low speeds.

The SLE, SLT, and AT4 models qualify for the bed-view camera, universal garage door opener, and both Driver Alert packages.

Denali ($66,495: 2500HD, $67,695: 3500HD) is also exclusively a Crew-cab model with all-wheel drive. It doesn’t have the dedicated off-road equipment but packs virtually every other upgrade mentioned above. Plus an 8-inch driver information display, chrome grille and side mirror housings, 20-inch alloy wheels, front/rear parking sensors, almost all the cameras, both Driver Alert packages, navigation, wireless charging, and the Bose audio system.

There is, however, still the opportunity to splash more cash on a new Sierra HD Denali. An Ultimate package adds a powered sunroof, Rear Camera Mirror, and the 15-inch color head-up display. The Denali Black Diamond Edition brings an auxiliary trailer camera, trailer tire pressure monitoring, front/rear floor liners with removable carpet inserts, power-retractable steps with LED perimeter lighting, a Kicker audio system, and 20-inch alloy wheels finished in high-gloss black.

Other options for the 2021 Sierra HD range include LED roof marker lights, E85 flex-fuel capability, soft tonneau cover, side-bed storage, lockable vault, up fitter switches, and snowplow preparation.


The 2021 Sierra HD comes with a traction control system (TCS), Stabilitrak with trailer-sway control, four-wheel disc brakes with anti-lock braking, hill start assist, plenty of airbags, and a programmable Teen Driver key. Additional safety and driver assistance systems are available at most trim levels and standard in the Denali.

For example, the Driver Alert Package I comes with front/rear parking sensors, lane-change alert, and blind-spot monitoring with rear cross-traffic alert. Driver Alert Package II includes forward-collision warning with automatic emergency braking, lane departure warning, automatic high beams, following-distance indicator, and a Safety Alert Seat.

Behind the Wheel

It wouldn’t be the first choice for casual commuting because of its size, but driving the Sierra HD is a pleasure. A long trip would be an enjoyable cruise. In terms of comfort and convenience, the Sierra HD excels. It’s also quiet and roomy inside.

The steering system is a hydraulically assisted recirculating-ball setup with optional digital assistance. An independent front suspension enhances steering precision and maneuverability while contributing to comfort levels. The rear suspension is a stalwart solid axle with 3-stage, multi-leaf springs.

With or without a load in the bed or a trailer attached, the Sierra HD handles well and rides smoothly. The base gasoline V8 is perfectly adequate, but the diesel V8 is the MVP.

Its torque is impressive and the 10-speed transmission makes use of it in every gear. And it’s still wonderfully refined, with only a hint of diesel engine clatter when it’s asked to work really hard.

There’s a ton of technology to make towing easier. The ProGrade Trailering system can be configured with up to 15 camera views, including the magical transparent-trailer view, which synthesizes multiple camera shots into a single moving image that gives the illusion of seeing right through the trailer. It’s not perfect (motorcycles and distant vehicles are tricky), but it’s nevertheless comforting to see what’s behind.

Other extremely useful views make hooking up a trailer much easier. And cameras can even show what’s inside the trailer, allowing drivers to check on the cargo during a trip. The trailering app can also interface with certain makes of trailers to control and monitor functions like HVAC or water and waste management.

Other Cars to Consider

2021 Ford Super Duty — Starting at $35,925, the Super Duty has an even torquier diesel engine, plus massive towing and payload abilities.

2021 Ram HD — Starting at $35,790, the Ram HD has arguably the nicest interior of the class.

2021 Chevrolet Silverado HD — Starting at $36,295 and based on the same platform as the Sierra HD, the Silverado has many of the same features and benefits.

Autotrader’s Advice

Once you determine your towing and hauling requirements, along with your desire for advanced and luxury features, you can see which heavy-duty truck is most suitable. There are really no bad choices. The SLT version of the 2021 Sierra HD is a good balance of features and expenditure, and it’s eligible for many desirable options. Make sure there’s enough in the budget for both Driver Alert packages. Find a 2021 GMC Sierra 2500HD for sale or find a 2021 GMC Sierra 3500HD for sale

Colin Ryan
Colin Ryan specializes in writing about new cars. But he has also covered trucks, vans, 3-wheelers, even the occasional motorbike. That’s the kind of thing that happens while contributing to the Los Angeles Times, Autotrader, Kelley Blue Book, Popular Mechanics, Variety, Mazda and Lexus customer magazines, as well as many enthusiast sites and publications. He was also a staff writer at BBC Top... Read More about Colin Ryan

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