GMC 2009 Sierra 1500 Crew Cab Owner's Manual page 130

1 (First): For the Hydra-Matic
this position reduces vehicle speed even more than
2 (Second) without using the brakes. You can use it on
very steep hills, or in deep snow or mud. If the shift
lever is put in 1 (First) while the vehicle is moving
forward, the transmission does not shift into first gear
until the vehicle is going slowly enough.
For an Allison Transmission
transmission, this position reduces vehicle speed
without using the brakes. You can 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 1 (First) it provides the
lowest gear appropriate to current road speed and
continues to downshift as the vehicle slows, eventually
downshifting to 1 (First) gear.
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.
2-32
®
4-Speed transmission
® ®
or Hydra-Matic 6-Speed
Range Selection Mode (Allison
®
Hydra-Matic 6-Speed Transmission)
The vehicle may have a Range Selection Mode.
The Range Selection Mode helps control the vehicle's
transmission and vehicle speed while driving down hill
or towing a trailer by letting you select a desired range
of gears.
®
or