2021 GMC Sierra 2500HD

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The Car Connection Expert Review

Aaron Cole Aaron Cole Managing Editor
August 4, 2020

Buying tip

If you’re looking for an off-road truck and need to save a few bucks, the X31 package offers most of the hardware without the AT4’s price.

features & specs

2WD Crew Cab 159"
2WD Crew Cab 159" SLE
2WD Crew Cab 159" SLT
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The 2021 GMC Sierra Heavy Duty pickup lineup is impressive in its capability and performance.

The 2021 GMC Sierra Heavy Duty pickup hog mollies are back this year—how could you miss them? Mechanically related to the Chevrolet Silverado HD twins, the GMC versions are comparatively a little more rock ‘n’ roll. New this year are versions of the pickup that take it further off-road (X31) and take it further into superlative naming schemes (Denali Black Diamond). It’s still offered in 2500 and 3500 versions, with single- or dual-rear-wheel configurations, with one of two V-8 engines. Regular-, double-, and crew-cab configurations are available, the last of which is more popular with retail shoppers.

It’s a 7.0 on our rating scale with two important asterisks—heavy-duty pickups aren’t rated for fuel economy or safety. If scored, it would almost certainly sink that number; the truck lacks standard active safety features found on many other new cars and its fuel-economy figures are roughly “LOL.” (Read more about how we rate cars.)

The GMC Sierra HD unabashedly punches a huge hole in the wind. After last year’s update, the heavy-duty pickup added girth and grandeur, most notably in its huge, upright grille that can be lacquered with acres of chrome.

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The body sides are equally impressive for their length and mass. GMC does little to hide the truck’s mass—it’s fine.

A 6.6-liter gas V-8 is standard and makes 401 horsepower. It’s paired to a 6-speed automatic transmission and can lug more than three tons in the bed if needed. A 6.6-liter turbodiesel is a pricey upgrade but comes with eye-popping stats: 445 hp, 910 lb-ft, up to 35,500 pounds of towing. It’s teamed to a smooth 10-speed automatic and better for it.

Crew cabs are more common and are very comfortable places to be for up to five adults. GMC offers short- or long-bed setups (except regular-cab pickups, which only offer a long bed) and its deep and wide bed holds plenty. A trick tailgate is fitted on most trucks and it’s helpful—provided you don’t bang it into a trailer hitch.

Like last year, the Sierra HD is offered in base, SLE, SLT, AT4, and Denali trim levels that start at about $42,000 and run past $80,000. Like other heavy-duty competitors, no two GMC Sierra HDs need to be the same, although most shoppers have considered the crème de la crème: Sierra HD Denali with the optional turbodiesel engine. They’re nice places to be, and they’re also bigger than some apartments.


2021 GMC Sierra 2500HD


We want it both ways: Impressive on the outside and inside. The Sierra HD excels at the former.

Updated last year, the 2021 GMC Sierra HD is a brute. Its massive shoulders and incredibly tall face are only overshadowed by the truck’s sheer size and weight—more than 22 feet long and up to four tons in some configurations. It’s a macho, macho truck that only gets more ostentatious in Denali trim. Its exterior is bold and impressive, but the Sierra HD’s interior is a letdown. It’s a 6 for style.

The big grille is tall and imposing and draws a line to the bulging hood scoop that feeds air into the big motor. The LED headlights are sharp and draw around the grille that flexes the truck’s enormous power. The lower front bumper can be massively chromed and it sits on top of tow hooks that can be black, red, or yep, more chrome.

The sides of the Sierra HD are mostly flat, although the bottoms tuck in. Around back, most pickups will get a multifunction tailgate that’s useful—once you figure out the right combination of buttons to get what you need open.

Inside, the GMC Sierra HD should be the uptown cousin of the Chevrolet Silverado HD, but it doesn’t always succeed. The dash and interior materials are soft in top trims, but it’s not convincingly luxurious nor worth the added cost. Almost impossibly, the truck’s 8.0-inch touchscreen gets lost in the dash—surrounded by vents and some blank plastics that feel too thin. Compared to crosstown rivals from Ford and Ram, the GMC and Chevrolet trucks are a step behind inside.  

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2021 GMC Sierra 2500HD


Two stout V-8 engines offer incredible capability in the Sierra HD.

Two engines offer mighty capability in the 2021 GMC Sierra Heavy Duty pickups, but the ride is only so-so. Starting from an average score of 5, the Sierra Heavy Duty gets another point added to its bruising V-8 engines. It’s a 6.

GMC offers its heavy-duty trucks in 2500 and 3500 configurations, the latter available with a dual-rear-wheel setup. Rear-wheel drive is standard, and four-wheel drive is a popular upgrade. Two rear axle ratios are available, depending on need, and the turbodiesel V-8 is available with an integrated power take-off to power machinery such as farm equipment.

The base gas engine is a 6.6-liter gas-powered V-8 that makes 401 hp and 464 lb-ft of torque. It’s tops for payload, and can carry 7,442 pounds in dual-rear-wheel spec or 4,534 pounds in single-rear-wheels spec. The gas engine is paired to a 6-speed automatic transmission.

An optional 6.6-liter V-8 turbodiesel is available and it’s the towing champ. It makes 445 hp and 910 lb-ft and can haul a fifth-wheel trailer up to 35,500 pounds or up to 20,000 attached to a conventional hitch. It’s paired to a smooth 10-speed automatic transmission that’s well-suited for long hauls.

Both engines confidently propel the truck, although the diesel engine is supremely confident with a trailer attached. It’s a costly upgrade—more than $9,000 on some trucks—although GMC estimates more than half of shoppers will opt for it.

Like other big trucks, the GMC Sierra HD is a handful around town. The long body and sheer size make it difficult to maneuver, although a variable-ratio steering rack helps somewhat.

The Sierra HD uses an independent front suspension that’s geared toward ride comfort, which many other competitors skip. When unladen, the big truck’s choppy ride is hard to miss. It’s another sign that these trucks are best when put to work.  

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2021 GMC Sierra 2500HD

Comfort & Quality

Big enough to bring the team and tow the court.

The 2021 GMC Sierra HD carries cargo like few vehicles can—more than 17.5 tons of it, if you have that much.

Up to five people fit in crew-cab models in supreme comfort, too. The Sierra HD lacks the polish of rivals from Ram and Ford, but our comfort scale mostly skips that. It’s a 9 for comfort.

The Sierra HD is available in regular-, double-, or crew-cab configurations with a short or long bed behind it, depending on the number of seats. Regular cabs are rare, and crew cabs are the norm. Our rating is based on those.

The Sierra HD was new last year, and it can be impossibly long—up to 22.5 feet from tip to tail. The front seats are wide and accommodating, and interior material spans base cloth to supple leather. In the rear seats of crew-cab models, there are more than 43 inches of leg room for very tall riders.

Crew-cab models have more storage possibilities than The Container Store. A wide, deep center console offers USB chargers, there’s more storage underneath the rear seats, and there are storage compartments in the seats as well.

There are two bed sizes, depending on cab configuration. Regular cab models get an 8-foot bed; double cabs and crew cabs offer a 6-foot-6 or 8-foot bed.

The beds are deep and wide, and four-by-eight sheets of building material can lay flat in the box. Inside the bed are 12 tie-downs and a 120-volt power outlet. Many trucks will feature an integrated multi-folding tailgate that can make getting into the bed easier. Fully deployed, it can bang against some trailer hitches, but it’s a useful feature that has plenty of practical uses.

Most Sierra HDs are well-equipped, although the interior materials are a step behind rivals from Ford and Ram.

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2021 GMC Sierra 2500HD


The Sierra HD skips crash-tests.

There may not be a wall robust enough, nor a budget big enough, to ruin a 2021 GMC Sierra Heavy Duty in the name of science. If either of those conditions is met, we’ll update this space. For now, it’s incomplete.

Active safety features such as automatic emergency braking and active lane control are on the menu, but they’re not standard fare. The same goes for other common-sense features such as parking sensors, blind-spot monitors, and up to 15 available camera views to make hitching and towing easier.

The GMC Sierra HD’s broad work- and luxury-truck missions make it hard to offer standard safety gear across the board, but automatic emergency braking should be a common denominator. Every truck should have that by now. Tsk, tsk.


2021 GMC Sierra 2500HD


Most trucks are well-equipped, but the GMC Sierra HD Denali is like no other.

There’s a 2021 GMC Sierra HD for just about every truck-related need, including the needs we didn’t know we had.

Starting from an average score, the truck gets a point for plentiful options and another for plentiful camera views on some trucks that make towing a breeze. It’s a 7.

There’s not enough time or enough ink on the internet to dive into what’s possible for the 2021 GMC Sierra, so what follows is the abridged version.

Equipment doesn’t change much between 2500 and 3500 trucks—that’s mostly a designation for how much gear it can haul. Base trucks start close to $42,000 and are rare sights on dealer lots; they’re trimmed for work detail and not much else. Regular-, double-, and crew-cab configurations are available and covered above. Most retail shoppers will opt for crew cab models, so we’ll assume that’s the pick here.

The Sierra 2500 HD SLT with four-wheel drive is our sane pick for its features, value, and capability. It costs about $58,000 and includes a trick tailgate, leather upholstery, heated front seats, an 8.0-inch touchscreen for infotainment with Apple CarPlay and Android Auto compatibility, four USB ports, Bluetooth, 18-inch wheels, and a 6.6-liter V-8. Myriad options are available for the truck including paint, wheels, axle configurations, powertrains—it’s impressive. Up to eight cameras offer 15 different views to help guide the truck into tight parking spaces, hitch up a trailer, or confidently reverse a boat into the lake. It’s a worthwhile feature that’s standard or available on most trucks.

Sierra AT4 and Denali editions are available to tempt well-heeled buyers looking for tough or tony heavy-duty pickups, respectively. They’re luxurious and well-equipped, luxury cars in their own rights.

This year, a pair of new special editions are the only noteworthy changes for equipment: A Denali Black Diamond edition adds premium audio by Kicker and 20-inch wheels; a Sierra HD X31 version is a more affordable off-road model.

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2021 GMC Sierra 2500HD

Fuel Economy

The 2021 GMC Sierra HD lacks official mileage estimates.

Heavy-duty trucks like the 2021 GMC Sierra HD don’t report fuel-economy estimates to the EPA. Without that, we can’t assign a score here.

Brace yourself for news you knew was coming already: the big haulers from GMC are prolifically thirsty, based on our real-world drives. Low teens around town are possible, but single digits are too—regardless of what’s under the hood. On the highway, the Sierra HD can settle into a lope around the high teens, but that’s without a trailer attached. Lug super-size trailers and the Sierra HD can gulp fuel. Crew-cab models are fitted with a 36-gallon fuel tank that at least extends the distance between fuel-station visits, but it won’t make them any less painful.

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