A carry-over from 2006, the 2007 Sierra 2500HD offers up to six-passenger seating in WT, SL, and SLT trim levels. The standard engine is the 6.0Liter V8 that produces 300HP and 360LB-Ft of torque. There is also a 6.6Liter V8 turbo-charged DuraMax diesel engine with an Allison six-speed automatic transmission offered as an option on all models.