GMC 2011 Sierra Owner's Manual page 329

On vehicles with this feature, you
can change the position of the
throttle and brake pedals.
No adjustment to the pedals can
be made when the vehicle is in
R (Reverse) or while using cruise
control.
The control used to adjust the
pedals is located on the instrument
panel below the climate control
system.
Press the bottom of the control to
move the pedals closer. Press the
top of the control to move the
pedals away.
Before you start driving, fully
press the brake pedal to confirm
the adjustment is right for you.
While driving, make only small
adjustments.
The vehicle may have a memory
function which lets pedal settings
be saved and recalled. See
more information.
for
The ignition switch has four different
positions.
To shift out of P (Park), the
ignition must be in ON/RUN or
ACC/ACCESSORY and the regular
brake pedal must be applied.