2021 GMC Sierra AT4 Specs
8 powertrain configurations on federal record for the 2021 GMC Sierra AT4: 6.2L 8-cyl Premium Gasoline; 3.0L 6-cyl Diesel; 5.3L 8-cyl Regular Gasoline, rated up to 24 MPG combined by the EPA.
Source: EPA federal records (fueleconomy.gov) · Updated 2026-10-26 · By CarWhere Research
| Engine | Transmission | Drivetrain | City | Highway | Combined |
|---|---|---|---|---|---|
| 6.2L 8-cyl Premium Gasoline | Automatic 10-spd | 4-Wheel Drive | 15 | 19 | 17 |
| 3.0L 6-cyl Diesel | Automatic 10-spd | 4-Wheel Drive | 22 | 26 | 24 |
| 5.3L 8-cyl Regular Gasoline | Automatic 10-spd | 4-Wheel Drive | 16 | 21 | 18 |
| 5.3L 8-cyl Regular Gasoline | Automatic 8-spd | 4-Wheel Drive | 16 | 21 | 18 |
| 5.3L 8-cyl Regular Gasoline | Automatic 6-spd | 4-Wheel Drive | 14 | 18 | 16 |
| 5.3L 8-cyl Regular Gasoline | Automatic 8-spd | 4-Wheel Drive | 14 | 20 | 16 |
| 6.2L 8-cyl Premium Gasoline | Automatic 10-spd | 4-Wheel Drive | 14 | 19 | 16 |
| 5.3L 8-cyl Regular Gasoline | Automatic 10-spd | 4-Wheel Drive | 15 | 21 | 17 |
Sierra AT4 by year
Buying a used Sierra AT4? Specs are the easy half.
then check the specific car: the Full VIN Report shows that VIN's factory build, recall record, and market history before you pay for it.
Frequently asked questions
What engines does the 2021 GMC Sierra AT4 have?
3 engines on federal record: 6.2L 8-cyl Premium Gasoline; 3.0L 6-cyl Diesel; 5.3L 8-cyl Regular Gasoline, offered with Automatic 10-spd, Automatic 8-spd, Automatic 6-spd and 4-Wheel Drive. The full per-configuration table is above.
What gas mileage does the 2021 GMC Sierra AT4 get?
EPA combined ratings run 16–24 MPG depending on configuration — the table above shows city/highway/combined for each engine, transmission, and drivetrain.
How do I get the specs for my exact VIN?
These are the federal-record configurations for the 2021 GMC Sierra AT4 overall. For one specific vehicle — its exact engine, trim, factory options, and original window sticker — decode the 17-character VIN free at carwhere.com/tools/vin-decoder.
Where does this data come from?
The U.S. EPA's public vehicle dataset (fueleconomy.gov) — the federal record of every US-market configuration since 1984 — refreshed 2026-10-26. Public-domain data; republish with attribution to CarWhere (carwhere.com).