The 2007 Chevrolet Silverado Classic 2500HD LT3 Extended Cab 4WD has a standard 6.0 L, 300 hp V8 engine with 4 speed automatic transmission.  This trim has 4 doors, seats 5, and tows up to 12000 lbs.  Think of the LT3 as the premium trim in the lineup with its leather seats and Bose sound with cd changer.