The GMC Sierra (and its Chevrolet Silverado twin) has changed little since its 1999 debut. Our tested Z71 Silverado had a stiff, choppy ride--other trim lines ride slightly better. Braking is adequate, and fit and finish are unimpressive. The powertrain isn't as smooth as competing models from Toyota or Nissan. The Sierra's assets are a selectable, full-time, four-wheel-drive system and a generous load capacity. The Denali is an expensive AWD model with a 6.0-liter V8. A hybrid version of the extended cab is available in some states, with a claimed 12 percent boost to fuel economy.