Massive 2020 GMC Sierra 2500 HD gets AT4 off-road gear

All-new heavy-duty pickup has loads of power plus adventure potential

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The GMC Sierra 2500HD is at home on the worksite as it is on a dusty trail | Bob Golfen

Full size and then some, the all-new GMC Sierra Heavy Duty pickup impresses not only with its powerful capability but with its refined drivability, a gentle giant able to tote or tow huge loads while still coddling the driver and passengers inside its spacious cabin.

New for 2020 is GMC’s AT4 off-road package applied to the 2500HD/3500HD pickup trucks, making them bona fide work and play vehicles on the grandest of scales. 

The test truck was a 2020 GMC Sierra 2500HD AT4, a 4-wheel-drive crew-cab model completely loaded with premium options, including a Duramax 6.6-liter turbo-diesel V8 that’s linked with the standard Allison 10-speed automatic transmission.

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The Sierra is packed with towing features | GMC

Quite a mighty machine, and while I was not personally equipped to test out its towing capacity (which as noted is huge), I was looking forward to some plus-size fun on the rugged desert trails in the hills north of Phoenix, Arizona. 

Alas, that was not to be as my time with the Sierra was hampered by seriously stormy weather that resulted not only in squishy off-road conditions but actual dangerous flooding.  There are few things in the desert as daunting as a normally dry wash turned into a rushing torrent.   Quite a few people required rescuing.  I did not want to be one of them.

But I did get to drive the Sierra HD quite a bit, albeit on paved roads, and it performed admirably as a luxury vehicle cruising the open highway.   At one point, the GMC did some actual truck work, carrying a load of furniture and such as I helped my son move (between rainstorms) across town.

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Fording a (small) stream | GMC

The ride’s a bit jiggly on its heavy-duty suspension, but the 2500 performs well at highway speed with a stable and confidence-inducing ride.  It’s quiet inside, too, the better to hear the awesome Bose premium sound system. 

There’s some diesel clatter while driving around town, but it quiets down to an underlying hum at speed.  The 10-speed trans – which must be a mind-boggling array of movement inside its aluminum case – performs seamlessly so that you’d never know it was pretty much continuously shifting up and down unless you look at the numbers displayed on the dashboard.

While the Sierra HD drives nicely, I never could shake the awkward feeling of piloting such an immense craft.  The seat position feels as high as a semi (not quite) and its size and heft are hard to ignore when driving through traffic or turning into small streets.   Parking lots are a challenge and the best strategy is to immediately choose an outlying spot.

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The Sierra crew cabis more than 20 feet long

So no, this would not be a vehicle for anyone who doesn’t require its strong capacities.  Towing a big boat, a large camper or a trailer loaded with worksite supplies comes to mind, as does carrying a load of heavy equipment or materials. 

But with its lofty price tag, as much as a luxury sedan, the 2500HD AT4 most likely would not be a truck driven by a tradesman or construction worker.  More likely, the owner of the construction business. 

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This was hammered home (pun intended) when I stopped to take photos of the truck at a home-construction site, where a small but high-end neighborhood is being built.  A woman in a pricey SUV pulled up, lowered the window and asked if I was the owner of the development.  I doubt she would have assumed that were I driving a lesser truck.

The Sierra came with a protective bra to protect its grille | Bob Golfen

That Duramax turbo-diesel V8 is a beast, by the way, rated at 445 horsepower and a massive 910 pound-feet of torque at just 1,600 rpm.  From a standstill, the 7,700-pound truck feels light as a Mini when you step on the throttle and trundle off.  It should be able to shrug off pulling the heaviest loads – it is rated, after all, for towing 18,500 pounds.   It can carry more than 3,500 pounds in its bed.

If you require a heavier suspension and chassis setup, the 3500HD moves those capacities up a few notches.

The 2500HD AT4 boasts an array of electronic gear to enhance drivability, towing and off-roading, including an off-road suspension with Rancho Shocks, skid plates and Eaton locking rear differential; 18-inch wheels with Michelin all-terrain tires (the test truck had 20-inchers as part of a Premium Package); Traction Select System with Off-Road mode; Hill Descent Control and Hill Start Assist; 15-inch diagonal Head-Up Display with Off-Road Inclinometer; and HD Surround Vision for low-speed views of vehicle surroundings.

The dashboard is well-organized and intuitive | GMC

The Surround Vision includes a low-angle camera in the front so that while off road you can see on the central video screen what’s directly in front of the truck instead of just peering over the broad hood and hoping for the best, or stopping and getting out to examine what’s ahead. It works at low speeds such as when crawling over rough terrain.

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The Sierra 2500 HD AT4 comes very well-equipped with a base price of $57,700.  The test truck came with more than $19,000 worth of options, the biggest being the upgrade from the standard gasoline V8 to the diesel, a $9,890 item.  The AT4 Premium Package, priced at $4,215, includes a number of desirable driving, convenience and entertainment features besides the off-road gear. 

The Technology Package adds $2,125, the power sunroof is $995, and a Driver Alert Package is $645, The truck also was fitted with a Gooseneck/5th Wheel Package, at $545. 

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Cushy leather seats were fitted front and rear | GMC

With $1,595 shipping and minus an ATM Premium Package Discount (whatever that means) the bottom line hit $76,960. 

Pickup trucks keep getting bigger and more capable, with domestic models from GMC, Chevrolet, Ford and Ram still leading the charge in size and power.  Ford and Ram have similar off-road treatments as the GMC AT4 for their heavy-duty pickups, which add a dose of fun and adventure to the trucks’ workhorse natures.

2020 GMC Sierra 2500HD AT4

Vehicle type: five-passenger, crew-cab pickup truck, 4-wheel drive
Base price: $57,700 Price as tested: $76,960
Engine: 6.6-liter turbo-diesel V8, 445 horsepower at 2,800 rpm, 910 pound-feet of torque at 1,640 rpm Transmission: 10-speed automatic
Wheelbase: 159 inches Overall length/width: 250 inches / 81.85 inches
Curb weight: 5,140 pounds Gross vehicle weight: 10,800 pounds
EPA mileage estimates: NA
Assembled in: Flint, Michigan

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Bob Golfen is a longtime automotive writer and editor, focusing on new vehicles, collector cars, car culture and the automotive lifestyle. He is the former automotive writer and editor for The Arizona Republic and SPEED.com, the website for the SPEED motorsports channel. He has written free-lance articles for a number of publications, including Autoweek, The New York Times and Barrett-Jackson auction catalogs. A collector car enthusiast with a wide range of knowledge about the old cars that we all love and desire, Bob enjoys tinkering with archaic machinery. His current obsession is a 1962 Porsche 356 Super coupe.

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