GMC 2011 Sierra Owner's Manual page 345

If your vehicle has the Allison
Transmission, or the Hydra-Matic
6-Speed Automatic Transmission,
it has a Low Traction Mode that
can assist in vehicle acceleration
when road conditions are slippery,
such as with ice or snow. While
the vehicle is at a stop, select the
second gear range using Range
Selection Mode. This will limit
torque to the wheels after it detects
wheel slip, preventing the tires from
spinning.
Vehicles with an automatic
transmission have a Tow/Haul
Mode. The Tow/Haul Mode adjusts
the transmission shift pattern to
reduce shift cycling, providing
increased performance, vehicle
control, and transmission cooling
when towing or hauling heavy loads.
The selector button is located on
the end of the shift lever. Turn
the Tow/Haul Mode on and off
by pressing the button. When
the tow/haul is on, a light on the
instrument panel cluster will
come on.
See
for more information.
Also see Tow/Haul Mode under
for more information.