2021 GMC Sierra AT4 Duramax Review

Christian Wardlaw, Independent Expert | Mar 19, 2021

Introduction - Find the best GMC deals!

General Motors distinguishes the 2021 GMC Sierra from the 2021 Chevrolet Silverado through design and a handful of exclusive features. Typically, the GMC is bolder in appearance, with squared-off styling and more chrome trim. And the popular, luxury-themed, GMC-exclusive Denali trim levels are about as close as you can get to a modern Cadillac pickup truck. 

Otherwise, the Sierra and Silverado are one and the same. Since we last reviewed a Sierra in 2019, GMC has made steady improvements to its large light-duty pickup. In 2020, the company made the following changes:

  • 8-speed and 10-speed automatic transmissions became available with the 5.3-liter V8 engine
  • New AT4 and Denali CarbonPro Editions debuted with carbon-fiber composite cargo bed
  • Camera-based adaptive cruise control became available
  • Bed View Camera debuted
  • High-definition surround-view camera became available, with two trailering camera provisions
  • New SiriusXM 360L satellite radio expanded entertainment options

Now, for the 2021 model year, GMC makes additional changes to the Sierra:

  • Multiple new camera systems to enhance towing and hauling activities
  • Improved towing capacity for turbocharged gas 4-cylinder and turbocharged diesel 6-cylinder engines
  • Expanded availability of MultiPro tailgate design
  • Wireless Apple CarPlay and Android Auto are available

For 2021, the GMC Sierra lineup continues with regular, extended, and crew cab styles with short, standard, and long cargo box lengths. Depending on the configuration, you can choose between standard, SLE, Elevation, SLT, AT4, and Denali trim levels.

Previously, J.D. Power reviewed the 2019 GMC Sierra Denali. This review focuses on the Sierra’s changes since then, the AT4 trim level, the Duramax diesel engine option, and how they potentially impact its overall appeal to consumers.

What Owners Say About the GMC Sierra - Find the best GMC deals!

2021 GMC Sierra AT4 Black Front Quarter View

Photo: Christian Wardlaw

According to data collected from verified owners for the J.D Power 2020 Automotive Performance, Execution and Layout (APEAL) Study, 90% of GMC Sierra owners are male, matching the large light-duty pickup segment. The median age of a Sierra owner is 58 years (vs. 54).

Owners say their favorite things about the Sierra are (in descending order) the:

  • Exterior styling
  • Powertrain
  • Driving feel
  • Feeling of safety
  • Setting up and starting

Owners indicate their least favorite things about the Sierra are (in descending order) the:

  • Getting in and out, in a tie with interior design
  • Driving comfort
  • Infotainment system
  • Fuel economy

In the J.D. Power 2020 APEAL Study, the Sierra ranked number two out of five large light-duty pickups.

What Our Independent Expert Says About the GMC Sierra - Find the best GMC deals!

In the sections that follow, our independent expert provides an analysis of a Sierra Crew Cab equipped with a short cargo bed, 4-wheel drive, and AT4 trim. Additionally, the test truck had the following options:

  • Ebony Twilight Metallic paint
  • AT4 Premium Package
  • AT4 CarbonPro Edition Package
  • Technology Package
  • Power sunroof
  • Rear under-seat storage
  • All-weather floor liners 

The price of the tested Sierra AT4 came to $66,955, including the $1,695 destination charge.

Duramax Diesel is a Downright Deal 

2021 GMC Sierra AT4 Duramax Diesel Engine

Photo: Christian Wardlaw

Unlike Ford and Ram, General Motors makes its optional turbodiesel engine affordable. And at just $995, it’s a genuine bargain considering its effortless ability to deliver 21.1 mpg in testing. That’s short of the EPA’s 24-mpg rating, but I wasn’t going easy on the throttle, and much of my driving involved mountainous terrain.

The turbocharged 3.0-liter inline 6-cylinder diesel engine is a gem. It makes 277 horsepower at 3,750 rpm and 460 lb.-ft. of torque starting at a low 1,500 rpm. Dubbed the Duramax, it matches the Sierra’s most powerful V8 engine option for torque but delivers it much sooner than does the 6.2-liter gas engine.

This year, GMC increased the Duramax diesel’s towing capacity. Depending on the configuration, it can tow up to 9,300 pounds and haul as much as 2,150 lbs. of payload. As tested, in AT4 crew cab 4-wheel-drive specification, the ratings are 8,800 lbs. and 1,810 lbs., respectively.

A 10-speed automatic transmission expertly distributes the power to the Sierra’s wheels. From a standstill, or when pressing harder on the accelerator pedal after rounding a turn or when passing slower vehicles, there is a momentary delay as the turbocharger spools up, followed by a flood of torque that makes the Sierra quite enjoyable to drive – especially at elevation.

AT4 Specification Preps Sierra for Serious Off-Roading

If you’re planning off-roading excursions, you’ll want to consider the Sierra AT4. In addition to a 2-inch factory suspension lift and an off-road-tuned suspension with Rancho shocks, the Sierra AT4 equips the truck with a 2-speed Autotrac transfer case, an automatic locking rear differential, and skid plates. Mud-terrain Goodyear Wrangler DuraTrac tires are available for people who are serious about venturing off the pavement in all kinds of weather.

Those tires whir loudly on the highway, but they’re effective in the muck, as I discovered bouncing around on a rain-soaked and rutted trail. Better yet, the AT4’s suspension modifications improve the Sierra’s ride and handling regardless of the type of road. Thanks to the X31 Off-Road Package, you can enjoy these benefits in any Sierra except for the Denali, which has an exclusive adaptive damping suspension. 

Impressive Tech Presented in Hit-and-Miss Fashion

2021 GMC Sierra Head Up Display Adaptive Cruise Control

Photo: Christian Wardlaw

During the past two years, GMC has added several technology enhancements to the Sierra. 

In 2020, a camera-based adaptive cruise control system became available, and the photo above shows the system in action via the Sierra’s optional 15-inch head-up display. As such technology goes, the adaptive cruise in the Sierra is remarkably smooth and sophisticated, able to respond to changing traffic conditions without behaving in an abrupt, hesitant, or unrefined manner.

Additionally, GMC has improved the infotainment system with SiriusXM 360L satellite radio, which offers dramatically expanded entertainment choices. Wireless Apple CarPlay and Android Auto are newly available for 2021, and it works well while eliminating the clutter associated with wired smartphone mirroring technology.

However, GMC needs to improve its overall infotainment game. The maximum touchscreen display size is eight inches, which is smaller than what Ford and Ram offer. Also, the Sierra’s top Bose audio system is woefully uncompetitive against the best from the competition.

Notably, during testing week, high winds in Southern California caused widespread power and internet outages. The Sierra’s active 4G Wi-Fi hotspot subscription and its household-style dashboard power outlet turned the truck into a mobile office. All it needed was a more convenient way to work on a laptop while sitting in the driver’s seat.

You Want Cameras? The 2021 GMC Sierra has Cameras. Lots of ‘Em

One of the new wars within truckdom is the race to see who can put the most payload-hauling and trailer-towing cameras on their pickups. Ford started the fight, Ram dove in, and General Motors followed suit shortly after the current-generation Silverado and Sierra went on sale for the 2019 model year.

In 2020, the Sierra added these optional features:

  • Trailer-tow mirrors
  • Surround-view camera with two provisions for trailering cameras
  • Bed-view camera with two provisions for trailering cameras

For 2021, GMC builds on these features with:

  • Jack-knife Alert – Warns the driver if sensors determine that a jack-knife threat exists
  • Trailer-length indicator – Helps the driver to understand if vehicles are in the trailer’s blind spot
  • Rear Trailer View – Adds new guidelines and a trailer-angle indicator showing the relationship of the trailer to the truck
  • Rear Side View – Upgraded to offer a split side view to both sides of the truck when reversing (previously worked only when moving forward)
  • Cargo Bed View – Upgraded to include a zoom function and a new bed hitch guidance function

In total, GMC claims the Sierra offers up to 15 different camera views. Pair the surround-view camera with an extra trailer-mounted camera and a transparent trailer view “erases” your trailer so that you can see what’s behind it. A “bowl view” vantage point shows the Sierra and its surroundings, helping a driver negotiate tight situations. Cameras help drivers attach trailers, see what’s in front of the truck, check the load in the bed, and even see what’s happening inside a trailer.

I didn’t tow anything and cannot comment on how effective these cameras are under those conditions. But it’s worth pointing out that both Ford and Ram also offer semi-autonomous trailer reversing technology, while General Motors does not.

Independent Expert Opinion - Find the best GMC deals!

2021 GMC Sierra AT4 Black Rear Quarter View

Photo: Christian Wardlaw

The 2021 GMC Sierra AT4 looks good, offers plenty of utility, and makes owning a diesel-powered light-duty pickup mighty affordable. The ride and handling are better than the Sierra’s standard suspension, and the optional mud-terrain tires make the truck feel unstoppable in the slop. GMC also offers numerous useful technologies for the Sierra, though in some cases, it appears to be falling behind on the tech curve.

Equipped with the Duramax diesel, the Sierra solves the fuel economy complaints voiced by the people who own this truck. But nothing short of an interior gut and redesign will address some of the other issues that Sierra owners tell J.D. Power are among their least favorite things about their trucks.

Christian Wardlaw is a veteran digital automotive journalist with over 25 years of experience in test-driving vehicles. In addition to JDPower.com, his work has appeared in numerous new- and used-car buying guides, newspapers, and automotive industry trade journals.

The opinions expressed in this review are the author’s own, not J.D. Power’s.

No portion of these reviews may be reproduced, distributed, publicly displayed, or used for a derivative work without J.D. Power’s written permission. © 2022 J.D. Power

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