Large fender flares stretch away from the body to cover the 35-inch-tall BFGoodrich tires. At the rear, the cargo box features lockable, lighted storage compartments, along with a number of tie-down cleats, including a pair in the bed floor and two on each side of the bed. A non-slip rubber pad is used on the tailgate, while two special compartments inside the cargo box provide access to a 110-volt power outlet and air compressor. A composite bed liner with a unique "circuit board" pattern provides a protective cover for the bed.

Motorized, deployable assist steps for the cab and cargo bed make it easier to enter and exit the All Terrain HD, while maximizing ground clearance during off-road driving. It also incorporates a number of industrial-grade lighting elements to provide greater visibility for safer driving where stars may be the only other source of illumination. The lighting details include:

• High-intensity LED headlamp, taillamp and fog lamp lighting mounted in impact-resistant composite housings and featuring edge-lit illumination
• High-intensity LED park and turn signal lamps
• Smooth-appearance front marker lamps integrated behind the top edge of the windshield glass
• Integrated center high-mounted stop lamp and rear marker lights mounted at the top edge of the rear window glass
• LED floodlights for the cargo bed and assist steps.

The All Terrain HD is painted Iridium Metallic - a dark charcoal color that reveals a reddish, anodized inflection when viewed from certain angles. It complements other anodized and satin-metal finishes on the exterior, which give the truck a more precise and functional appearance.

The interior matches the exterior aesthetic, with premium appointments and increased functionality, including enhanced lighting. It conveys solidity and precision, blending accent details such as stainless steel mesh and satin chrome with an amplified expression of the All Terrain's premium features. Two-tone dark gray leather seats, matched with embossed carbon fiber-style leather on the seating surfaces, have red contrast stitching. Additional leather-wrapped interior features include the steering wheel, instrument panel and center console.

A new navigation radio is also featured on the Sierra All Terrain HD concept and previews future radios to be offered in GMC vehicles. An integrated 80-gig hard drive contains map data for the navigation system. It eliminates the need for a map disc and provides greater storage of music from portable devices. It also features DVR-style "time lapse playback," which allows up to 20 minutes of recording/playback from the AM/FM/XM radio stations.

All Terrain Chassis and Suspension

Based on the chassis of the 2011 Sierra HD trucks, the All Terrain HD features a fully boxed steel frame with exceptional strength and torsional stiffness. It incorporates the production models' new independent front suspension and asymmetrical rear leaf-spring suspensions, but with a wider 73-inch (1,853 mm) track (front and rear) that enhances stability during off-road and highway driving. A production Sierra 2500HD has front and rear tracks of 68.8 inches (1,748 mm) and 67.3 inches (1,709 mm), respectively.

An increased ride height provides greater ground clearance of 21.1 inches (536 mm) at the rockers and 11.8 inches (300 mm) at the skid plates, while specialized Fox off-road shocks deliver exceptional damping on tough terrain. They were created specially for the All Terrain HD, with specific valving. The shocks feature visible, remote fluid reservoirs - connected to the shock bodies via custom hoses - mounted in the wheel house liners and are matched with front and rear jounce shocks. They add additional compression damping and more controlled rebound, which helps increase control, stability and handling.

The All Terrain HD also features electronic disconnection of the front stabilizer bar, which enables greater crawling capability on rocky terrain. The driver simply pushes a button inside the cab to disconnect it from the front suspension.

Custom upper and lower control arms for the front suspension are designed to work with the Fox off-road shocks and jounce shocks, while supporting the greater ground clearance and ride height. They contribute to the wider track, as do the aggressive 20-inch machined aluminum all-terrain wheels. The wheels are deep, with six split-spoke elements, and are constructed in a reverse drop-flange method that ensures optimal strength. They also feature a mix of satin chrome and anodized aluminum finishes, which provide durability and a premium appearance that complements the body's Iridium Metallic color.

A full composite underbody protection system shields the All Terrain HD's transmission, drivetrain, fuel tank, exhaust system and axle differentials. It starts with the front bumper, which rolls beneath the truck and leads to a composite, integral belly pan that covers a front suspension skid plate. Protective covers are also mounted beneath the driveline components, while the front and rear differentials feature direct-mounted skid plates. The rear bumper is integrated with the rear skid plate.

Powertrain Details

The Sierra All Terrain HD concept is propelled by the new, production 6.6L Duramax turbo-diesel V-8 and Allison 1000 six-speed automatic transmission powertrain combination offered in the 2011 Sierra HD trucks. The Duramax is rated at 397 horsepower (296 kW) and 765 lb.-ft. of torque (1,037 Nm).

The powerful 6.6L Duramax is more fuel-efficient - with up to 11-percent greater fuel economy than previous versions - and reduces NOx emissions by up to 63 percent. The powertrain's efficiency is assisted by the Allison 1000 transmission, which requires less engine power to funnel torque to the axles. It also incorporates a "smart" exhaust brake feature that helps save wear on the brakes on downhill grades, a feature available on production Sierra HDs.

With the same proven powertrain as production Sierra HD trucks, the All Terrain HD delivers comparable hauling and towing capabilities, including:

• Estimated payload capacity of 2,700 pounds (1,225 kg)
• Estimated conventional towing capacity of 13,000 pounds (5,896 kg)
• Estimated fifth-wheel towing capacity of 15,600 pounds (7,076 kg).

The Sierra All Terrain HD also features four-wheel drive, with automatic locking front and rear differentials, while the 14-inch, four-wheel disc brake system from the production Sierra HD provides the stopping power for this unique off-roader.

GMC Sierra All Terrain HD Concept: Photo Gallery, Review (1/2) and Specifications