Used 2021 GMC Sierra 3500 HD Double Cab

The 2021 GMC Sierra HD pickup truck range was all-new last year. Along with its Chevy Silverado HD stablemate, this is one of the freshest heavy-duty trucks available.

It comes in 2500 HD and 3500 HD forms, representing differences in towing and payload capabilities. The former can tow 18,500 pounds and carry 3,863 pounds. The latter’s top pulling power is 20,000 pounds with a conventional trailer or 36,000 pounds with the diesel engine/fifth-wheel/ dual rear wheel configuration. And maximum payload is 6,610 pounds.

Every variant of the 2021 Sierra HD, however, is strong and powerful. Unlike heavy-duty pickups from Ram and Ford, the GMC Sierra HD has an independent front suspension for optimum ride comfort. Its bed is also close enough to the ground for easy loading/unloading.

With muscular V8 engines complemented by a ProGrade Trailering System that takes much of the stress out of towing, the 2021 GMC Sierra HD can work hard while insulating its occupants in a serene and spacious cabin.

With either engine, even when pulling a load, the 2021 Sierra HD cabin is remarkably tranquil. This truck feels big because it is, but a well-controlled ride and an overall refinement add to driver confidence. An independent front suspension provides comfort (even under load), excellent maneuverability, and some reassuring steering feel. Naturally, a high seating position provides a commanding view of the road, and a relatively large (15 inches diagonally) head-up display is great to have.

Both 6.6-liter V8s, gasoline or diesel, feel absolutely right in the Sierra HD, working effortlessly and well isolated from the cabin. Anyone planning serious towing (like the majority of heavy-duty truck owners) should consider the Duramax 6.6-liter diesel V8 with the sturdy Allison 10-speed automatic transmission, which will propel the Sierra HD from standstill to 60 mph in 19.9 seconds — when pulling an 18,000-pound trailer.

Even so, the direct-injected gasoline V8 (with a 6-speed automatic) is certainly not lacking. With gasoline V8, there’s no need to refill a Diesel Exhaust Fluid (DEF) tank every 5,000 to 7,000 miles. But this process is simple enough because the DEF filler is next to the diesel filler instead of under the hood.

GMC’s ProGrade Trailering System takes the stress out of hooking up and towing a trailer. The Technology Package has up to 15 camera views, allowing the driver to see the bed, hitch, trailer sides, around the trailer, and even inside it. Transparent Trailer View stitches images together to create an excellent virtual picture of what’s behind the trailer.

This year sees the addition of a jack-knife alert, a trailer length indicator where the center screen shows if there are any vehicles behind and to the sides that might hinder a lane-changing maneuver, a rear trailer view/trailer-angle indicator with guidelines for reversing with a trailer, rear side view enhancement with split left/right images of the trailer when reversing, plus a cargo bed zoom view/bed hitch guidance feature to help align and connect to a gooseneck/fifth-wheel trailer.

The 2021 GMC Sierra HD, particularly in Crew Cab form, enjoys outstanding headroom and legroom. As well as a comprehensive array of gauges (including a handy readout for brake pad life), the Sierra HD offers a large head-up display (HUD) and a user-friendly touch-screen infotainment system.

The Denali version is especially lavish, its interior highlighted by premium leather seating surfaces with large pebble grain and contrast stitching, along with dark aluminum trim and open-pore wood.

The off-road-focused AT4 has darkened trim complemented by textured aluminum finishes on the steering wheel, center stack, and sill plates. The seats are covered in Jet Black leather with perforated inserts of Kalahari tan. The headrests are also embroidered with an AT4 logo.

The 2021 Sierra HD also offers a Rear Camera Mirror, a first among heavy-duty pickups. With the flip of a switch, the rearview mirror transforms into a video screen that shows a full wide-angle view of what’s behind, without any rear headrests obstructing the view.

The 2021 Sierra HD pickup won’t be mistaken for any other truck, thanks to GMC emblazoned across the grille in bold red letters. Large proportions and a hood with a prominent (and functional) scoop all contribute to the Sierra HD’s commanding presence. Built-in steps behind the cab and on the rear bumper enable easy access to the bed.

For primary lighting, the GMC Sierra HD features LED headlights and taillights, plus prominent C-shaped LED strips as the daytime running lights. Amber side-marker lights are integrated into the lips of all four fenders. The Denali treatment includes a grille and side mirror housings finished in chrome.

Roof-marker lights are standard on all dual-rear-wheel Sierra HDs and all Denali versions of the Sierra HD, except where prohibited by law.

SMART TRAILER INTEGRATION
With the myGMC App (or Apple CarPlay/Android Auto), this system allows Sierra HD owners to monitor and control a range of smart systems in their suitably equipped recreational trailers. This includes water tank levels, air conditioning, and the power slide-outs.

INTEGRATED ENGINE EXHAUST BRAKE
The diesel V8 has an integrated engine-exhaust brake, what big-rig truckers call a “Jake brake.” With the press of a button, the engine’s backpressure attenuates speed on steep descents, reducing the load on the brakes. This exhaust brake also works with the cruise control, allowing a set speed to be maintained over hilly terrain.

The 2021 Sierra HD comes in base, SLE, SLT, AT4, and Denali trim levels. Base and SLE models are available with regular, Double, or Crew cabs. The SLT comes with a Double or Crew cab (these cabs have a Rear Seat Reminder as standard). The AT4 and Denali come solely with the Crew cab.

Bed lengths are standard (6.8 feet) or long (8.2 feet); the regular cab comes solely with the longbed. In 3500 HD form, only the Crew cab is available with either bed. The others have the longbed.

The base 2021 Sierra 2500 HD has 17-inch steel wheels, vinyl floor covering, manual locks, LED headlights/daytime running lights/taillights, a rearview camera, manually adjustable front seats, corner step, bed step, cargo area light, height-adjustable steering wheel, single-zone air conditioning, Apple CarPlay/Android Auto smartphone integration, 7-inch infotainment touchscreen, and two USB ports. It’s pretty sparse, but rival trucks follow the same kind of formula. And it is eligible for several driver assistance features.

A drivetrain consisting of the Duramax 6.6-liter diesel V8 and Allison 10-speed automatic transmission is the main option for the 2021 GMC Sierra HD.

To obtain more indulgent items like carpeted flooring, leather-wrapped steering wheel, power-adjustable side mirrors, Wi-Fi, and 17-inch alloy wheels means going for at least the SLE trim. The SLT is more attractive, with 10-way power-adjustable front seats, heated steering wheel, variable steering assistance, dual-zone automatic climate control, wireless smartphone integration, satellite radio, and rear under-seat storage.

The off-roading AT4 comes with a specialist suspension featuring Rancho shock absorbers, skidplates, and a 2-speed automatic transfer case with an automatic locking rear differential. And 20-inch Goodyear Wrangler Territory tires become available this year.

The luxurious Denali brings 20-inch alloy wheels, heated/cooled/leather-covered front seats, driver assistance features, a 360-degree high-definition camera system, bed-view/trailer-view cameras (also newly standard for 2021), wireless smartphone charging, and a 7-speaker Bose audio system.

A Denali Ultimate package adds a Rear Camera Mirror, a head-up display, and a powered sunroof. The new-for-2021 Denali Black Diamond Edition includes an auxiliary trailer camera, trailer tire pressure monitoring, power-retractable steps with LED perimeter lighting, Kicker audio system, and 20-inch alloy wheels finished in high-gloss black.

Other options include a gooseneck/fifth-wheel package with stamped bed holes and a 7-pin trailer harness, plus a Driver Alert Package II that includes forward-collision alert with automatic emergency braking, lane-departure warning, and automatic high beams.

Torque is the thing with heavy-duty pickups. It’s the motivational muscle. The 2021 GMC Sierra HD does fairly well in this respect. Buyers can choose a direct-injected 6.6-liter gasoline V8 with 464 lb-ft of torque or a turbodiesel 6.6-liter V8 with a mighty 910 lb-ft of torque.

Rear-wheel drive (RWD) is the basic configuration, 4-wheel drive (4WD) is available as an option. However, the AT4 and Denali variants have 4WD as standard.

The gasoline V8 connects to a 6-speed automatic transmission; the diesel V8 is linked to a 10-speed automatic transmission supplied by Allison, a well-respected 3rd-party manufacturer.

The Environmental Protection Agency (EPA) does not calculate any fuel economy estimates for trucks of this size.

6.6-liter V8
401 horsepower @ 5,200 rpm
464 lb-ft of torque @ 4,000 rpm
EPA city/highway fuel economy: N/A

6.6-liter turbodiesel V8
445 horsepower @ 2,800 rpm
910 lb-ft of torque @ 1,600 rpm
EPA city/highway fuel economy: N/A