GMC 2010 Yukon XL Denali Owner's Manual page 158

When temperatures are very cold, the Hydra-Matic
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.
M (Manual Mode) : 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 the vehicle warranty. If you are stuck,
do not spin the tires. When stopping on a hill, use
the brakes to hold the vehicle in place.
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 throttle position, vehicle load, and hill grade.
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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.
The 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.