At the North American International Auto Show this year, the biggest buzz surrounded the largest concept there: GMC's Sierra All Terrain HD, an off-road-biased truck based on the 2011 Sierra HD platform. We sat down with Carl Zipfel, manager of GM's Advanced Truck Studio, to see if this dream vehicle can become a reality.

Why It Can
This concept was based on a crew-cab 2011 Sierra 2500HD. The idea was to build on the strengths of the HD chassis and powertrain and take the production model in other directions. The design group rallied around one specific sketch, executed as a full-size clay model. Parts were prototyped, and the vehicle was done in eight months. "We were able to do this one pretty fast because it's mostly production-based," Zipfel said. "It uses the production chassis, cab, and powertrain. All the design work focused on the off-road components and the front and rear clips of the vehicle."

It Doesn't Use A New Engine And Transmission
There were no major changes to the powertrain: It's the 397-horse, 6.6-liter Duramax turbodiesel, with the Allison 1000 six-speed automatic. The engineers and designers made the most significant changes to the suspension, body, and styling -- all of which, Zipfel explained, were focused on making a realistic, yet highly capable off-road version of the Sierra HD. Most of the parts were prototyped and built at the UAW shops within the Warren, Michigan, design center. These facilities include a mechanical assembly, fabrication shop, wood shop, model shop, and a plaster shop for the molds. The shops have all the tools needed to create a vehicle from the ground up. Parts don't even have to be sent out for chrome.

Body Mods Are Realistic
This layout is a crew cab 2500 that uses GM's shortest bed -- the 68-inch-long unit. This bed isn't available on the HD models; for the concept, this item started out as the short bed from a 1500, but by the time they were done, it was its own unique fiberglass bed. But we wouldn't be surprised if this third bed were eventually added to the options list for the three-quarter ton.