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