While 24 MPG combined won’t break any fuel economy records, it’s a good mix of capabilities, comfort, and relatively low fuel consumption for the 2021 GMC Sierra 4WD AT4 with the 3.0L Duramax diesel engine. This truck isn’t for someone obsessed with saving every drop of fuel. It’s for people who need a strong work vehicle during the week and a comfortable ride for weekend trips. The AT4 trim is made for off-road enthusiasts who want ruggedness and a powerful look, and for them, 24 MPG is an acceptable compromise.

City and highway performance

The EPA estimates for the 2021 GMC Sierra 4WD AT4 with the 3.0L Duramax diesel and 10-speed automatic transmission are 22 MPG in the city and 26 MPG on the highway. The city figure shows how the Sierra’s weight and four-wheel-drive affect fuel use in stop-and-go driving. However, the diesel engine’s torque helps it accelerate easily, and the smooth-shifting transmission makes the most of the engine’s power. The Sierra really performs well on the highway. The 10-speed transmission lets the engine run at low RPMs, which increases fuel economy during long drives. Drivers will enjoy the quiet, comfortable ride and the ability to travel long distances without frequent gas stops. Find all all Gmc fuel economy data on FuelEconomyHub.com.

Annual fuel cost

The EPA estimates that the annual fuel cost for the 2021 GMC Sierra 4WD AT4 3.0L diesel is $2,300. This is based on driving 15,000 miles per year and assumes a fuel price that reflects the national average. Your actual fuel cost will depend on current prices in your area and your driving habits. If you drive much more or less than 15,000 miles per year, your fuel costs will change. Still, the $2,300 estimate gives a good idea of the overall cost of owning this truck.

Real-world expectations

While the EPA estimates are a good starting point, real-world fuel economy can change based on different things. Driving hard, towing often, and going off-road will all lower fuel efficiency. On the other hand, accelerating gently, driving at consistent speeds on the highway, and keeping tires properly inflated can help you reach or even go beyond the EPA estimates. Payload also matters.

Keep in mind that the AT4 is made for heavy-duty use, and using it to its full potential will affect how efficiently it uses fuel. The 3.0L Duramax diesel has been known to provide mileage close to its EPA estimates, but watching your own driving habits is still the best way to know what to expect.

How it compares

The 2021 GMC Sierra 4WD AT4 3.0L diesel does well in fuel economy compared to other full-size trucks with four-wheel drive. A similar gasoline-powered Sierra with a 5.3L V8 often struggles to reach 20 MPG combined. A Ford F-150 with the 3.0L PowerStroke diesel gets similar numbers, around 23-25 MPG combined, while the Ram 1500 EcoDiesel gets around 24 MPG combined. These comparisons are important for buyers who are thinking about the fuel efficiency trade-offs that come with a truck that has both off-road ability and full-size utility. For more information on SIERRA MPG across all years check out our site.

Tips to maximize efficiency

Watch the flow of traffic and avoid accelerating and braking suddenly. The Sierra’s diesel engine provides a lot of low-end torque, so you don’t need to push the gas pedal hard to get up to speed. Accelerating smoothly and gradually will save fuel and reduce wear on the truck.

Check and keep the tires at the right pressure regularly. Tires that don’t have enough air create more rolling resistance, which lowers fuel economy. Check your tire pressure at least once a month and fill them to the level shown on the door jamb sticker.

Don’t let the engine idle. If you’re going to be stopped for more than a minute or two, turn off the engine. Idling uses fuel without moving the truck, and it can greatly lower your overall fuel economy, especially in city driving.

If possible, remove any extra weight from the truck bed or cargo area. Extra weight lowers fuel efficiency, so only carry what you need. Also, think about taking off roof racks or cargo carriers when you’re not using them, since they can create drag and lower fuel economy.