The 2018 GMC Sierra 1500 used two automatic transmissions depending on engine: a six-speed automatic with the base 4.3-liter V6 and an eight-speed automatic with the 5.3-liter and 6.2-liter V8. A diesel option was not offered in the 2018 model year.
In detail, the transmission pairing varied by engine option and trim, shaping performance, towing capability, and efficiency. The following breakdown focuses on the gas-engine Sierra 1500 lineup for 2018 and the transmissions that paired with each engine.
Transmissions by engine
Explanation of the list: this section maps each 2018 Sierra 1500 engine to its standard automatic transmission.
- 4.3L V6 EcoTec3 — 6-speed automatic transmission.
- 5.3L V8 EcoTec3 — 8-speed automatic transmission.
- 6.2L V8 EcoTec3 — 8-speed automatic transmission.
Conclusion: The 4.3L V6 used a six-speed automatic, while both V8 options used an eight-speed automatic across most trims, with no diesel option available in 2018.
Diesel option and model-year context
The Duramax diesel engine was not offered in the 2018 Sierra 1500; GM introduced a 3.0-liter Duramax turbo-diesel in the 2019 model year for the Silverado/Sierra 1500 lineup. This means the 2018 model year did not include a diesel transmission pairing.
Trim and drivetrain nuances
Across the 2018 Sierra 1500 lineup, the transmission pairing generally followed engine choice: the base 4.3L V6 with the six-speed automatic, and the 5.3L and 6.2L V8s with the eight-speed automatic. Most trim levels and configurations adhered to this mapping, though there could be minor variations by market or option packages. All transmissions were designed to handle two- or four-wheel-drive configurations without requiring different hardware for the different drive layouts.
Summary
In summary, for the 2018 GMC Sierra 1500: the 4.3L V6 uses a six-speed automatic, while the 5.3L and 6.2L V8 engines use an eight-speed automatic. A diesel option was not available in this model year, and the transmission choice is driven primarily by engine rather than by trim level alone.