2021 GMC Sierra Review: AT4 Trim and Duramax Diesel Add Appeal

GMC's diesel engine option makes the 2021 Sierra more compelling.

2021 GMC Sierra 1500Christian Wardlaw

Article QuickTakes:

When shopping for a full-size, light-duty pickup truck, your choices are limited to six brands. Nissan is one option, but Ford, General Motors, Ram, and Toyota are the dominant players. GM splits its fortunes between the 2021 Chevrolet Silverado and the 2021 GMC Sierra.

To distinguish GMC from Chevrolet, GMC markets Sierra as a "professional grade" choice and gives it exclusive features. This includes a carbon-fiber composite cargo bed option that resists scratches and dents while reducing weight and adding payload capacity. Whether the Sierra is truly professional grade and is worth the buy compared to a Chevy Silverado takes some consideration. Let’s dig into it.

To get a lay of the land with GMC Sierra, this truck comes in regular, extended (Double Cab), and crew cab styles with short, standard, and long cargo boxes. Two-wheel drive (2WD) is standard, but four-wheel drive (4WD) is an option except with the AT4 trim level (it’s included in the base price).

In its least expensive trim level, the truck is simply called Sierra. Depending on the cab and drivetrain configuration, buyers can upgrade to SLE, Elevation, SLT, AT4, and Denali specification. Multiple engines are available, ranging from a V6 and a couple of V8s to a turbocharged four-cylinder and a turbo-diesel six-cylinder.

Changes to the 2021 Sierra include increased tow ratings for the turbocharged engines, upgraded towing camera technology, a standard Multipro tailgate on all but the base Sierra, and a new Off-Road Package for the Sierra SLE, Elevation, and SLT. GMC also expands safety technology availability and offers new wireless Apple CarPlay and Android Auto connectivity.

For this review, GMC furnished a Sierra 1500 AT4 crew cab with a short cargo bed. It had the AT4 Premium, Technology, and Driver Alert II option packages, a CarbonPro bed, and a handful of additional options bringing the price at time of test drive to $66,695, including a $1,695 destination charge.

2021 GMC Sierra 1500Christian Wardlaw


Most GMC Sierras have too much decorative chrome. Perhaps this is one way for the more expensive GMC to compete with the Chevy Silverado—to make it fancier. However, the Elevation and AT4 trim levels suggest Sierra looks better without it. Our Sierra AT4 test truck's body-color trim, 2-inch suspension lift, 18-inch wheels with knobby mud-terrain tires, and purposeful red tow hooks made it look good on the outside.

On the inside, this GMC has an appearance that doesn’t quite meet expectations. Its wide panel joints and shut lines, bulging instead of flush control clusters, small 8-inch infotainment screen, and widespread shiny plastic are not justifying a price tag over $65,000. Even the leather feels stiff, dry, and rough; perhaps for durability instead of comfort.

Speaking of comfort, the Sierra doesn’t disappoint with broad, flat, power-adjustable front seats but the cushions aren't soothing in terms of how they support the body. GMC claims the Sierra offers more legroom and headroom than any other truck in the segment, but the reality is that many full-size, crew-cab trucks provide impressive amounts of space.

As a cold Pacific storm lashed California, the heated front and rear seats and heated steering wheel proved useful. Our AT4 test truck was also ready for hot weather, equipped with ventilated front seats and rear air conditioning vents.

Although the Sierra's interior looks outdated, the control layout is logical and intuitive. The infotainment system is easy to understand and use. Storage space is generous, but GMC could improve its amount, size, and innovation.

2021 GMC Sierra 1500Christian Wardlaw


In the realm of screen-size, GMC is losing ground. The largest available infotainment display measures 8 inches across, and it looks small on the Sierra's wide and tall dashboard. Appearances, however, do not reflect the system's level of sophistication. The Sierra's infotainment system is up to expected standards in the class, from its graphics and responsiveness to its slate of standard and available features.

New for 2021, available wireless Apple CarPlay and Android Auto make pairing a smartphone to the system even more effortless. Furthermore, if you're a fan of buttons and knobs, this system will suit you well with its offering. And if you're not, it has an excellent voice recognition system that is genuinely helpful. Despite its Richbass subwoofer, the Bose premium sound system needs to be better, especially at the test truck's price.

High winds caused a 36-hour power and internet outage while we had the Sierra. Moving our remote office into the truck was easy thanks to its handy, in-dash 110V power outlet and 4G LTE Wi-Fi hotspot. Although a center console work surface like what Ford offers in the new F-150 would've also proven useful.

As far as other technology goes, our Sierra offered a wide 15-inch head-up display, numerous trailer-towing camera views, and a digital rear camera mirror. The mirror was the least helpful visibility aid in this truck, ranking behind the parking sensors, reversing and surround-view cameras, and warnings for blind spots and rear cross-traffic.

Those last two features are part of the GMC Sierra's available advanced driving assistance systems (ADAS). This year, GMC makes forward-collision warning with pedestrian detection and forward automatic emergency braking available on all Sierras, expanding the availability of adaptive cruise control, lane-departure warning, lane-keeping assistance, and the company's vibrating Safety Alert Seat to all but the base trim level.

During testing, the adaptive cruise control and lane-keeping aids operated in a smooth and refined fashion with few false alerts. But the truck was slow to accelerate when changing lanes to pass slower vehicles. Most impressive, during twilight, the lane-keeping system identified lane markers that were nearly invisible from the driver's seat.

Unfortunately, the Sierra's crash-test ratings are not up to par. The National Highway Traffic Safety Administration (NHTSA) gives the Sierra a 4-star overall rating. At the same time, the Insurance Institute for Highway Safety (IIHS) assigns the front passenger's seating location a "Marginal" protection rating in a small overlap frontal-impact collision.

2021 GMC Sierra 1500Christian Wardlaw


With AT4 trim, GMC currently charges $995 to upgrade from the standard 5.3L V8 to its excellent turbocharged 3.0L inline six-cylinder diesel engine. Dubbed the Duramax, the diesel supplies ample torque, as much as the largest 6.2L V8 GMC offers for the Sierra. The torque is also more accessible, arriving at 1,500 rpm compared to 4,100 rpm for the 6.2L.

Unless you need this truck's maximum 11,800 lbs of towing capacity, or you simply cannot live without the rumble of a V8, the Duramax diesel is ideal. Supplying 277 hp and 460 lb.-ft. of torque, the diesel gives the Sierra AT4 9,300 lbs of towing capacity and a payload rating of 1,830 lbs.

Push the engine start button and there is a momentary delay before the diesel fires up with a traditional clatter. Shift the 10-speed automatic transmission into gear and the Duramax's turbo quickly spools up to serve a steady, unrelenting surge of acceleration. We ran the test truck from sea level to a mountain pass at 5,160 ft of elevation, and the Sierra AT4 effortlessly climbed that mile closer to the sky.

It also averaged 21.1 mpg without trying. While true that the result falls short of the official EPA estimate of 24 mpg in combined driving, it's much better than any of the Sierra's V8 engines can provide. We also ran the truck in automatic 4WD rather than 2WD which may have negatively impacted our number.

A short off-roading trip proved the Sierra AT4's mettle; the truck crossed deep ruts and navigated deep dips in a local trail without incident. We didn't encounter deep mud, but on wet muck the aggressive 18-inch Goodyear Duratrac tires and automatic 4WD made the Sierra seem invincible.

Back on pavement, the AT4's suspension is better than the stock underpinnings that GMC fits to the Sierra. The modifications firm up the ride and handling, eliminating most of the truck's unwanted body motions without unwanted brittleness.

In everyday driving situations, the mud-terrain tires offer adequate grip. They won't encourage you to take corners and curves with much speed. They also whir loudly, especially on the freeway, which you'll either find soothing or irritating.

2021 GMC Sierra 1500Christian Wardlaw


Styling is what sells the GMC Sierra. In terms of its quality, its construction, and for the most part its available features, it's the same truck as the Chevrolet Silverado.

What the Sierra needs to better compete is a nicer interior, improved technology, and better crash-test ratings. Though this truck's design is just three years old, the Sierra comes across as twice that age when measured up against the Ford and Ram. But that cost-effective diesel engine option sure helps to make up for shortcomings.

If you're a fan of both how this truck looks and its value-laden Duramax diesel, there is good news to report on other fronts. GMC confirms that the 2022 Sierra will get Super Cruise Level 2+ semi-autonomous driving technology late in its model year, along with digital instrumentation and a new dashboard that might be required to accommodate a larger infotainment system.

The winds of change are blowing strong at GMC with the new 2021 GMC Sierra.

This site is for educational purposes only. The third parties listed are not affiliated with Capital One and are solely responsible for their opinions, products and services. Capital One does not provide, endorse or guarantee any third-party product, service, information or recommendation listed above. The information presented in this article is believed to be accurate at the time of publication, but is subject to change. The images shown are for illustration purposes only and may not be an exact representation of the product. The material provided on this site is not intended to provide legal, investment, or financial advice or to indicate the availability or suitability of any Capital One product or service to your unique circumstances. For specific advice about your unique circumstances, you may wish to consult a qualified professional.
author photo
Christian Wardlaw
My first word was “car.” That’s what I’m told, anyway. For as long as I can remember, I’ve been obsessed with them. The design. The engineering. The performance. And the purpose. I’m a car enthusiast who loves to drive, but I’m also most interested in the cars, trucks, and SUVs that people actually buy. Anybody can tell you that a sports car is fast. What you need to know is whether or not you should buy that new SUV, and why. My life purpose is to help you make that decision.