GMC 2008 Chevrolet Tahoe Supplemental Owner's Manual page 16

MANUAL MODE (M): This position lets drivers select
the range of gears appropriate for current driving
conditions. If your vehicle has this feature, 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.
2-8
Range Selection Mode
The Range Selection Mode controls the vehicle's
transmission.
To use this feature, do the following:
1. Move the shift lever to the MANUAL MODE (M).
2. Press the plus/minus button, to upshift or downshift
selecting the desired range of gears for your current
driving conditions.