2008 GMC Sierra 1500 Pickup Owner's Manual - Page 105

MANUAL MODE (M): This position lets drivers select the range of gears appropriate for current driving conditions. See Range Selection Mode later in this section. Notice: Spinning the tires or holding the vehicle in one place on a hill using only the accelerator pedal may damage the transmission. The repair will not be covered by your warranty. If you are stuck, do not spin the tires. When stopping on a hill, use the brakes to hold the vehicle in place. Your vehicle has a shift stabilization feature that adjusts the transmission shifting to the current driving conditions in order to reduce rapid upshifts and downshifts. This shift stabilization feature is designed to determine, before making an upshift, if the engine will be able to maintain vehicle speed by analyzing things such as throttle position, vehicle load, and hill grade. If the shift stabilization feature determines that a current vehicle speed cannot be maintained, the transmission does not upshift and instead holds the current gear. In some cases, this may appear to be a delayed shift, however the transmission is operating normally. Your vehicle's transmission uses adaptive shift controls. Adaptive shift controls continually compares key shift parameters to pre programmed ideal shift conditions stored in the transmissions computer. The transmission constantly makes adjustments to improve vehicle performance according to the way the vehicle is being used, such as with a heavy load. During this adaptive shift controls process, some shifts may feel different as the transmission determines the best settings for a particular shift. 2-29