In short, the GMC Sierra 2500HD can be equipped with either a 6-speed automatic when paired with the gasoline 6.6L V8, or a 10-speed Allison automatic when paired with the 6.6L Duramax turbo-diesel. The exact setup varies by engine and model year.
Powertrain and transmission options
Two main configurations are used in the GMC Sierra 2500HD, depending on the engine.
Gasoline option
Gasoline powertrain pairing details.
- 6.6L V8 gasoline engine paired with a 6-speed automatic transmission.
The gasoline configuration emphasizes smooth daily driving and adequate towing capability, using a 6-speed automatic to manage power delivery.
Duramax diesel option
Duramax powertrain pairing details.
- 6.6L Duramax Turbo-Diesel V8 paired with an Allison 10-speed automatic transmission.
The Duramax diesel setup leverages the 10-speed automatic to maximize torque delivery and efficiency when towing heavy loads.
Performance context
Engine outputs vary by configuration: the gasoline 6.6L V8 typically produces around 401 horsepower and 464 lb-ft of torque, while the 6.6L Duramax turbo-diesel delivers about 445 horsepower and around 910 lb-ft of torque. The diesel’s 10-speed transmission helps keep the engine in its optimal torque range under heavy load.
Year and trim considerations
These transmissions have been used across recent GMC Sierra 2500HD model years, with calibration and software updates that can affect shift feel and towing performance. Always verify the exact transmission on a specific vehicle’s window sticker or with a dealer for the exact year and trim.
Summary
The GMC Sierra 2500HD offers two primary transmission choices aligned with its powertrains: a 6-speed automatic with the gasoline 6.6L V8, and a 10-speed Allison automatic with the 6.6L Duramax turbo-diesel. The choice influences towing capability, acceleration feel, and efficiency, and may vary by year and trim. For the precise configuration, check the vehicle’s build sheet or consult a GMC dealer.