GMC 2009 Yukon XL Owner's Manual page 138

D (Drive) can be used when towing a trailer, carrying a
heavy load, driving on steep hills, or for off-road
driving. You might want to shift the transmission to a
lower gear selection if the transmission shifts too often.
Downshifting the transmission in slippery road conditions
could result in skidding. See Skidding under Loss of
Control on page 4-11.
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 is 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 could 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 shifts stored
in the transmissions 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 might feel different as the transmission
determines the best settings.
2-32
When temperatures are very cold, the Hydra-Matic
6-Speed transmission's gear shifting could be delayed
providing more stable shifts until the engine warms
up. Shifts could be more noticeable with a cold
transmission. This difference in shifting is normal.
M (Manual Mode): This position is available on vehicles
®
with the Hydra-Matic 6-Speed transmission. It lets
drivers select the range of gears appropriate for current
driving conditions. If the vehicle has this feature, see
Range Select Mode (Hydra-Matic
transmission) later in this section.
3 (Third): This position is also used for normal driving.
It reduces vehicle speed more than D (Drive) without
using the brakes. You might choose 3 (Third) instead of
D (Drive) when driving on hilly, winding roads, when
towing a trailer, so there is less shifting between gears
and when going down a steep hill.
2 (Second): This position reduces vehicle speed even
more than 3 (Third) without using the brakes. You
can use 2 (Second) on hills. It can help control vehicle
speed as you go down steep mountain roads, but
then you would also want to use the brakes off and on.
If you manually select 2 (Second) in an automatic
transmission, the transmission will start in second gear.
You can use this feature for reducing the speed of
the rear wheels when you are trying to start the vehicle
from a stop on slippery road surfaces.
®
®
6-Speed