866-341-0624 The standard gas powerplant is a Vortec 6.0-liter V8 that is rated at 360 horsepower at 5,400 rpm and 380 lb-ft of torque at 4,400 rpm. The diesel-fueled alternative is a 6.6-liter V8 labeled Duramax, which is built for GM by Isuzu. This oil-burner makes 397 horsepower and a stump-pulling 765 lb-ft of torque at just 1,600 rpm.