17 MPG combined is what you can expect from high-torque, off-road-ready pickup trucks like the 2021 GMC Sierra 4WD AT4 with the 6.2L V8. This isn’t a truck for hypermilers; it’s for those who prioritize capability, sound, and the confidence from a reliable drivetrain. The AT4 buyer isn’t afraid of dirt roads, boat ramps, or the occasional snowstorm, and they likely have a specific need for the Sierra’s considerable towing and hauling abilities.

City and highway performance

The EPA estimates the 2021 GMC Sierra 4WD AT4 6.2L V8 will achieve 15 MPG in the city and 19 MPG on the highway. The city figure reflects the stop-and-go nature of urban driving, where the truck’s weight and large displacement engine demand more fuel to accelerate from a standstill. The highway figure, while better, still reflects aerodynamic realities and the energy required to maintain speeds over 60 mph. The 10-speed automatic transmission does its best to optimize fuel economy, but ultimately it cannot overcome the inherent thirst of a powerful V8 in a full-size truck.

Annual fuel cost

The EPA estimates an annual fuel cost of $3,400 for this specific Sierra configuration. This is based on driving 15,000 miles per year, with 55% of those miles driven in the city and 45% on the highway, at the national average fuel price. Your actual fuel costs will vary significantly depending on your driving habits, local fuel prices, and how often you use the truck’s four-wheel-drive system or towing capabilities.

Real-world expectations

While the EPA provides standardized testing, real-world MPG often differs. Owners of the 6.2L V8 Sierra AT4 frequently report numbers close to the EPA estimates when driven conservatively. However, aggressive acceleration, heavy towing, or consistent off-road use will lower fuel economy significantly. The sound of the V8 alone can tempt drivers to dip further into the throttle than strictly necessary, further affecting the MPG. Terrain also matters, significant hills or mountainous routes will decrease fuel economy compared to flat, open highway driving.

How it compares

Compared to other full-size trucks, the Sierra AT4 6.2L’s fuel economy is towards the lower end. A comparable Ford F-150 with the 3.5L EcoBoost V6, for example, can achieve around 20 MPG combined. Even the RAM 1500 with the 5.7L Hemi eTorque mild-hybrid system manages slightly better figures, landing around 19 MPG combined. You can view all Gmc fuel economy data to get a broader understanding of efficiencies. The Toyota Tundra, often criticized for its older powertrain, lands in a similar MPG range with its 5.7L V8, making the Sierra AT4’s fuel consumption less of an outlier in that context. This comparison matters because buyers often cross-shop these trucks, weighing factors like capability, features, and, of course, cost of ownership. If you’re interested in seeing specific SIERRA MPG across all years, we’ve got you covered.

Tips to maximize efficiency

Use the Sierra’s drive modes effectively. The default Auto mode prioritizes fuel efficiency in typical driving conditions. Switching to Tow/Haul mode or Off-Road mode will recalibrate the transmission and engine for those specific tasks, but will also increase fuel consumption. Only engage these modes when necessary.

Practice smooth acceleration and braking. Avoid abrupt starts and stops, as these actions waste fuel. Anticipate traffic flow and maintain a consistent speed whenever possible. Consider using cruise control on long highway stretches to minimize speed variations and optimize fuel economy.

Keep your tires properly inflated. Underinflated tires increase rolling resistance, which reduces fuel efficiency. Check your tire pressure regularly, especially during temperature changes, and inflate them to the recommended pressure listed on the doorjamb sticker.

Reduce unnecessary weight. Hauling around extra cargo adds strain to the engine and decreases fuel economy. Remove any unnecessary items from the bed of the truck or the cab. Even small weight reductions can contribute to improved MPG over time.

Consider the impact of modifications. Lift kits, oversized tires, and aftermarket accessories can negatively affect aerodynamics and increase weight, leading to reduced fuel economy. Choose modifications carefully, keeping in mind their potential impact on efficiency.