A truck brand based around professional grade performance, the 2006 GMC Sierra 2500HD receives strengthened diesel power. The Duramax 6.6-liter turbocharged diesel engine is radically upgraded for 2006. On available GMC Sierra models, an LBZ version of the 6.6-liter Duramax diesel is offered with a 650 pound-feet of torque output level. A six-speed Allison transmission is now available with the new Duramax diesel powerplants. The 2006 Envoy and the Yukon Denali are enriched with a host of added standard features including StabiliTrak electronic stability control. OnStar and cruise control has also been added to the Envoy. Two notable models have been excluded from the 2006 GMC selection. The Envoy XUV is discontinued for the 2006 model year. After a 20-year production run, the Safari minivan is no longer offered in the GMC model line-up. Along with certain products, GMC also withdraws availability of the innovative yet pricey Quadrasteer four-wheel steering system.