Aside from a new crew-cab version, 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 is unimpressive. The powertrain isn't as smooth as competing models from Toyota or Nissan. The Sierra's significant 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. The Quadrasteer four-wheel-steering system is a costly option that eases maneuverability in tight places. The HD (heavy duty) model is stiffer-riding.