As of 2011 the GMC and Chevrolet Heavy Duty models have being upgraded with a new fully boxed high strength steel frame from front to rear improving stiffness by 92% with bigger rear springs, larger engine and transmission mounts and new hydraulic body mounts to improve the ride. The front suspension incorporates new upper and lower control arms and new torsion bars tailored to one of five different gross axle weight ratings. Upper control arms are constructed from forged steel that is both stronger and lighter than the previous arms, while the new lower arms are cast iron to maximize load capacity. Using a unique torsion bar for each gross weight rating allows for better control over vehicle height, resulting in improved handling and better alignment for reduced tire wear. These improvements allow for up to a 6,000 pound front axle weight rating, allowing all 4wd trucks to accommodate a snow plow.