The four-door 2011 Sierra HD underpins the All Terrain concept, and power comes from The General’s 6.6-liter Duramax diesel V8. A six-speed automatic sends the 397 horsepower and 765 pound-feet of torque to all four wheels. Versus a normal Sierra HD, ground clearance has been increased by about three inches, width has been bumped up to 73 inches (four more than normal) and the whole package rides on 20-inch aluminum wheels wrapped in 35-inch BFGoodrich KM2 mud terrain tires. Off-road performance is enhanced with the addition of Fox off-road shocks (just like the Ford Raptor). Check out Autoblog.com for more info. and pics.