GMC 2010 Sierra 1500 Crew Cab Owner's Manual page 396

If the engine has stopped running, you need to
restart it. With the brake pedal pressed and the
parking brake still applied, shift the transmission to
P (Park) and restart the engine. Then, shift to
R (Reverse), release the parking brake, and slowly
back down the hill as straight as possible in
R (Reverse).
While backing down the hill, put your left hand
on the steering wheel at the 12 o'clock position so
you can tell if the wheels are straight and can
maneuver as you back down. It is best to back
down the hill with the wheels straight rather than in
the left or right direction. Turning the wheel too far
to the left or right will increase the possibility of a
rollover.
Things not to do if the vehicle stalls, or is about to stall,
when going up a hill:
Never attempt to prevent a stall by shifting into
N (Neutral) to rev-up the engine and regain forward
momentum. This will not work. The vehicle can roll
backward very quickly and could go out of control.
Never try to turn around if about to stall when
going up a hill. If the hill is steep enough to stall
the vehicle, it is steep enough to cause it to roll
over. If you cannot make it up the hill, back straight
down the hill.
5-20
If, after stalling, you try to back down the hill and decide
you just cannot do it, set the parking brake, put your
transmission in P (Park), and turn off the engine. Leave
the vehicle and go get some help. Exit on the uphill side
and stay clear of the path the vehicle would take if it
rolled downhill. Do not shift the transfer case to Neutral
when you leave the vehicle. Leave it in some gear.
Shifting the transfer case to Neutral can cause
your vehicle to roll even if the transmission is in
P (Park). This is because the Neutral position on
the transfer case overrides the transmission. You
or someone else could be injured. If you are going
to leave your vehicle, set the parking brake and
shift the transmission to P (Park). But do not shift
the transfer case to Neutral.