5.3L V8 was also made standard. The Vortec 6200 V8 was given wider availability, now being optional on LT and SLE Extended and Crew Cabs, completely supplanting the light-duty Vortec 6000 V8 in the process. The new Z71 Appearance Package was optional on LT and LTZ, it included: body-color grille and front fascia, body-color door handles and mirror caps, unique Z71 box side decals, chrome sill plates, and a unique Z71 gauge cluster. Two new exterior colors were added: Taupe Gray Metallic and Sheer Silver Metallic. For 2012, the Sierra and Silverado 1500 received another refresh. This time the Silverado was given new grille and front fascia treatments for both LT and LTZ models. A newly redesigned touch-screen navigation radio was optional on LTZ, SLT, and Denali. Trailer sway control and hill start assist are now standard on all models. Cooled seats were made optional on LTZ and SLT and the woodgrain trim was replaced with brushed aluminum. Heavy-Duty For the first time, the 8.1 L big block V8 is no longer offered on the Heavy-Duty models, and no replacement has been announced. The 6L90 6-speed automatic transmission is standard in all Heavy-Duty models. The Allison 1000 transmission is paired with the optional Duramax V8 diesel. As of 2011, the GMC and Chevrolet Heavy Duty models have been 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 snowplow. Additional front suspension enhancements come from new urethane bump stops, two per side. The upper shock mount has been changed from a single stem mount to a two-bolt design to eliminate the possibility of squeaks and thumps. The rear suspension design uses asymmetrical leaf