GMC released the third generation of the Sierra pickup-truck range in 2006 as a 2007 model-year for the 1500 series and the 2500 HD series in the following year as a 2008 model. GMC had over a century of experience on the market. It couldn't outsell the Ford F-Series, but it was close and offered an excellent platform able to pull more than the 1500 series. For the 2500 HD (heavy-duty), the American carmaker used a new platform, the T900, which replaced the T800 and offered better solutions and more powerful engines than its predecessor. Like its predecessor, the Sierra was available in a few body versions, starting with a chassis-cab and going up to the big crew-cab version. Its raked windshield at 57 degrees decreased the wind noise and the aerodynamic resistance, increasing the fuel-efficiency. To add a more dynamic appearance, the Sierra featured flared wheel-arches. The Regular Cab version featured a two-door cabin with either a bench or a pair of seats. The bed in the back was available in three sizes of 5.75' (1752 mm), 6.5' (1981 mm), and 8' (2438 mm) on three different wheelbases. Inside, the GMC Sierra offered two or three seating positions, depending on the trim level and options. Like most of the pickup-trucks on the market, it provided a big dashboard, with a steering-column mounted gear-selector for the automatic transmission. The manufacturer offered the Sierra with a choice of two engines paired as standard to a 4-speed automatic gearbox. It was available either as a 2WD or 4WD.