GMC 2011 Sierra Denali Owner's Manual page 265

WARNING
Driving to the top (crest) of a hill
at full speed can cause an
accident. There could be a
drop-off, embankment, cliff,
or even another vehicle. You
could be seriously injured or
killed. As you near the top of a
hill, slow down and stay alert.
If the vehicle stalls, or is about to
stall, and you cannot make it up
the hill:
Push the brake pedal to stop the
vehicle and keep it from rolling
backwards and apply the
parking brake.
If the engine is still running, shift
the transmission to R (Reverse),
release the parking brake, and
slowly back down the hill in
R (Reverse).
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.
Driving and Operating
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.
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.
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