http://VacavilleGMC.com (866) 593-1568 An optional 6.6-liter turbodiesel V8 is the engine of choice for those who plan on towing or hauling on a regular basis. This Duramax turbodiesel produces 397 hp and 765 lb-ft of torque and is mated to a beefier six-speed automatic transmission with manual shift control. In performance testing, a Sierra 2500HD with this engine accelerated from zero to 60 mph in a truly extraordinary 7 seconds. This engine uses a diesel exhaust fluid (DEF) injection system for cleaner emissions.