Overview
- GM published official 2027 fuel‑economy ratings on Thursday showing many V8‑equipped Silverado and Sierra 1500 configurations have lower highway and combined MPG than some 2026 models.
- The company says the drop comes from testing more representative customer setups such as larger tires, lifted suspensions, and added equipment that increase weight and drag and reduce fuel economy.
- Specifics include the 6.6L V8 ZR2 rated at 13 city / 15 hwy / 14 combined MPG with 481 hp, and the 5.7L 2WD rated lower than the 2026 5.3L despite higher power.
- On paper the 3.0L Duramax turbo‑diesel remains the most efficient option at 27 mpg highway and 24 mpg combined, giving an extended highway range thanks to a large fuel tank.
- GM has delayed official ratings for the base 2.7L TurboMax until early 2027 and independent real‑world MPG tests are still pending, which will help buyers judge how the new numbers play out in everyday use.