The GMC Sierra All Terrain HD concept is an exploration of heavy-duty truck capability combined with greater off-road versatility. It is highlighted by a bold exterior design, enhanced all-terrain suspension and premium details expected of a GMC - all designed to enable greater access to off-road destinations. The new 2011 Sierra HD underpins the All Terrain HD concept, with a modified, production-based 4WD chassis and the Duramax diesel/Allison 1000 six-speed powertrain. The enhanced suspension and... continue