A sporty SS version tops 2006 additions to these SUVs. TrailBlazer is the best-selling version of a GM design that also includes the Buick Rainier, GMC Envoy, Isuzu Ascender, and Saab 9-7X. TrailBlazer, Envoy, and Ascender offer five-passenger and extended-length seven-seat models; Rainier and 9-7X are five-seaters only. Extended TrailBlazers are called EXTs and, like regular-length models, come in LS and uplevel LT trim. All include antilock 4-wheel disc brakes, 4-speed automatic transmission, and a 291-hp inline 6-cyl engine. An optional 300-hp V8 includes GM's Active Fuel Management that automatically deactivates four cylinders while cruising to save fuel. LS and LT offer rear-wheel drive or GM's Autotrac 4WD, which can be left engaged on dry pavement and includes low-range gearing. GM's Stabilitrak antiskid system with rollover sensors is standard on all models. Newly available for five-passenger models, the SS package includes a 395-hp V8, sport suspension, and unique trim. It comes with 2WD or all-wheel drive without low-range gearing. Optional on all TrailBlazers are curtain side airbags that cover the 1st and 2nd seating rows. A DVD entertainment system and a navigation system are also optional.