The 2008 GMC Sierra Denali uses a six-speed automatic transmission, GM's Hydra-Matic 6L80, paired with the 6.2-liter V8 engine.
In the 2008 Denali, GM paired the top-trim Sierra with a modern, electronically controlled six-speed automatic designed for both two-wheel-drive and four-wheel-drive configurations. The 6L80 is the standard transmission for this setup, delivering smooth shifts and solid towing performance within the GMT900 platform.
Transmission type and year context
Designation and features
The Hydra-Matic 6L80 is a six-speed automatic transmission used by GM in many light- and heavy-duty trucks and SUVs. It offers overdrive, electronic control, and adaptive shift logic to optimize performance and efficiency with the 6.2L V8 engine found in the Sierra Denali of this year.
Drive configurations
The 2008 Sierra Denali was offered in both rear-wheel drive and four-wheel drive layouts. The 6L80 transmission is compatible with both configurations, paired to the vehicle’s transfer case when four-wheel drive is selected.
Context within the GM lineup
6L80 versus other GM six-speed options
For the 2008 GMT900 trucks, the 6L80 was the common six-speed automatic paired with the 6.2L V8 in the Denali. There are more robust, heavy-duty variants in GM’s lineup (such as the 6L90 used in some high-torque applications), but the Denali’s setup for that model year centers on the 6L80.
Summary
In 2008, the GMC Sierra Denali used a GM Hydra-Matic 6L80 six-speed automatic transmission, paired with the 6.2L V8, and available in both rear-wheel-drive and four-wheel-drive configurations. This combination provided modern shifting behavior and towing capability typical of that era’s high-end GM trucks.