The 2027 GMC Sierra mpg ratings are now posted on FuelEconomy.gov, and there is a detail worth checking before borrowing a number from a Silverado story: the two trucks do not match across every diesel configuration.
GMC’s 3.0-liter Duramax reaches 24 mpg combined and 27 highway with two-wheel drive. Its regular 4WD listing is 21 combined, one below the equivalent Chevrolet listing. The mud-terrain diesel entry also trails Chevy by one combined mpg.
Here is the Sierra 1500 breakdown from the EPA listings checked November 11, 2026. These figures cover the light-duty gasoline and diesel truck, not Sierra HD or Sierra EV.
Sierra diesel ratings run from 20 to 24 mpg combined
The 2WD diesel is the strongest Sierra entry for fuel economy among the engines currently listed. Four-wheel drive changes the calculation, and the EPA separates the mud-terrain version from the AT4X.
| 2027 configuration | City mpg | Highway mpg | Combined mpg |
|---|---|---|---|
| 3.0L diesel, 2WD | 22 | 27 | 24 |
| 3.0L diesel, 4WD | 20 | 23 | 21 |
| 3.0L diesel, 4WD with mud-terrain tires | 20 | 22 | 20 |
| 3.0L diesel, AT4X 4WD | 20 | 22 | 21 |
Sources: FuelEconomy.gov listings for the 2WD, 4WD, mud-terrain 4WD and AT4X. All four use a 10-speed automatic.
The Silverado diesel 4WD is rated at 21 city, 23 highway and 22 combined. Its mud-terrain version is 21/22/21, compared with the Sierra’s 20/22/20. The 2WD diesels match, as do the diesel Sierra AT4X and Silverado ZR2 at 20/22/21.
The database does not explain the cause of those brand differences, so we are not assigning them to weight, tires or aerodynamics. They are a reason to use the GMC entry when shopping for a GMC. Also, the published city, highway and combined values are rounded separately. Do not recalculate combined mpg by averaging the two displayed numbers.
The 5.7L and 6.6L V8s match Chevrolet’s ratings
Unlike the diesel entries, the Sierra’s V8 ratings line up with the corresponding Silverado configurations. The 5.7-liter 2WD is the highest-rated V8 combination at 17 mpg combined. At the other end, the mud-terrain 5.7L and the 6.6L AT4X each return a 14-mpg combined estimate.
| 2027 configuration | City mpg | Highway mpg | Combined mpg |
|---|---|---|---|
| 5.7L V8, 2WD | 15 | 19 | 17 |
| 5.7L V8, 4WD | 15 | 18 | 16 |
| 5.7L V8, 4WD with mud-terrain tires | 14 | 16 | 14 |
| 6.6L V8, 4WD | 14 | 18 | 15 |
| 6.6L V8, AT4X 4WD | 13 | 15 | 14 |
Source: FuelEconomy.gov’s 2027 GMC listings. All five use a 10-speed automatic. The EPA lists regular gasoline for the 5.7L and premium gasoline for the 6.6L.
There is a sizable spread within the AT4X alone: 21 mpg combined for the diesel and 14 for the 6.6-liter V8. That is useful information for someone who wants the off-road truck but still has a long commute. It does not, by itself, establish which engine costs less to own. Purchase price, local fuel prices, maintenance and how you use the truck still belong in that decision.
Check the truck’s label, and leave room for TurboMax
As of our November 11 check, the EPA’s 2027 GMC list did not include a Sierra 2.7-liter TurboMax fuel-economy entry. The published V8 and diesel figures therefore do not settle the four-cylinder comparison. A Canyon rating cannot fill that gap, even though it is another GMC pickup.
The EPA also uses configuration names such as “Mud Terrain Tires 4WD,” rather than listing every trim and option package in a shopper-friendly order. Keep those distinctions intact. Do not apply the basic 4WD figure to an AT4X or assume every off-road package receives the same number.
The bottom line: match the rating to your Sierra
Our 2027 Sierra specs and pricing coverage is a starting point for choosing a configuration. Before signing, compare its window sticker with the matching EPA entry. The diesel has the mpg advantage in the published Sierra lineup, but the difference between a 2WD truck, a mud-terrain model and an AT4X is too large to ignore.
