18 MPG combined is the reality check for anyone considering the 2021 GMC Sierra 4WD AT4 with the 5.3L V8. It isn’t a mileage master; it’s a truck built for capability, off-road ability, and a commanding presence. Owners prioritize these things and understand that fuel efficiency is less important, especially with standard four-wheel drive.

City and highway performance

The EPA estimates for the 2021 Sierra AT4 5.3L are 16 MPG in the city and 21 MPG on the highway. The city figure reflects the engine working harder to move this heavy truck through stop-and-go traffic. The 21 MPG highway rating is more achievable on long, steady cruises, but aggressive acceleration and higher speeds will quickly reduce that number. The 10-speed automatic transmission helps to optimize fuel economy by keeping the engine in its most efficient range, assuming you drive with a light foot.

Annual fuel cost

The EPA calculates the annual fuel cost for the 2021 GMC Sierra AT4 5.3L using a standard formula: 15,000 miles driven per year, combined fuel economy of 18 MPG, and national average fuel prices. Based on these assumptions, the estimated annual fuel cost is $2,450. Keep in mind that this is an average; your personal fuel costs will vary based on your driving habits, local fuel prices, and the actual miles you drive each year. Those who frequently tow or spend significant time off-road should budget for considerably higher fuel expenses.

Real-world expectations

The EPA ratings provide a useful baseline, but real-world fuel economy with the Sierra AT4 5.3L can change a lot. Drivers who spend most of their time in urban areas with frequent stops and starts may see numbers closer to or even below the 16 MPG city estimate. On the other hand, those who primarily drive on the highway, maintain consistent speeds, and avoid aggressive acceleration should be able to achieve or even slightly exceed the 21 MPG highway rating. Towing or hauling heavy loads will have a particularly detrimental impact on fuel economy, potentially dropping it into the low teens. Consider checking SIERRA MPG across all years for more information.

How it compares

The fuel economy of the 2021 Sierra AT4 5.3L places it squarely within the range of its competitors. A similarly equipped Ford F-150 with four-wheel drive and the 5.0L V8 engine achieves an EPA-estimated 17 MPG combined, a small difference. The Toyota Tundra, known for its reliability but not its efficiency, lags behind at around 14 MPG combined with its standard V8. Even the Ram 1500, often touted for its ride quality, only manages around 17 MPG combined with its comparable V8 and 4WD. These differences are unlikely to sway a buyer already set on the AT4’s specific blend of off-road equipment and GMC’s styling; for these buyers, other brands may be off the table and browsing all Gmc fuel economy data is irrelevant.

Tips to maximize efficiency

Practice smooth acceleration and braking. The Sierra AT4 is a powerful truck, but aggressive driving habits consume a lot of fuel. Anticipate traffic flow, avoid sudden stops, and accelerate gradually to save a noticeable amount of gas over time.

Maintain proper tire inflation. Underinflated tires increase rolling resistance, which forces the engine to work harder and reduces fuel economy. Check your tire pressure regularly and inflate them to the manufacturer’s recommended level, typically found on a sticker inside the driver’s side doorjamb.

Reduce unnecessary weight. Carrying extra weight in the bed or cab of the truck reduces fuel economy. Remove any unnecessary items to lighten the load and improve efficiency. Even seemingly small items can add up and impact your gas mileage.

Use cruise control on the highway. Cruise control helps to maintain a consistent speed, which can improve fuel economy on long highway drives. However, be mindful of hilly terrain, as cruise control can sometimes downshift aggressively on inclines, negating some of the fuel savings. If that happens, shift manually.

Consider switching to 2WD when conditions allow. The AT4’s four-wheel-drive system improves traction in challenging conditions, but it also increases fuel consumption. When driving on dry pavement, switch to two-wheel drive to reduce drivetrain drag and improve gas mileage. This is especially true for in-town driving.