Hummer H2 2010 Owner's Manual page 152

1 (First): This position reduces vehicle speed without
using the brakes. Use it for major/severe downgrades
and off-road driving where the vehicle would otherwise
accelerate due to steepness of grade.
When you shift to 2 (Second) or 1 (First) it provides the
lowest gear appropriate to your current road speed and
continues to downshift as the vehicle slows, eventually
downshifting to the selected gear.
The 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 vehicle speed, throttle position and vehicle
load. 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.
3-34
The transmission uses adaptive shift controls that
compares key shift parameters to pre-programmed ideal
shifts stored in the transmission's computer. The
transmission constantly makes adjustments to improve
vehicle performance according to how the vehicle is
being used, such as with a heavy load or when the
temperature changes. During this adaptive shift control
process, shifting may feel different as the transmission
determines the best settings.
When temperatures are very cold, the Hydra-Matic
6L80 automatic transmission's gear shifting may be
delayed providing more stable shifts until the engine
warms up. Shifts may be more noticeable with a cold
transmission. This difference in shifting is normal.
®