GMC Sierra Classic 2007 Owner's Manual page 378

Q:
Suppose, after stalling, I try to back down
the hill and decide I just cannot do it. What
should I do?
A:
Set the parking brake, put the transmission in
PARK (P), or the manual transmission in
FIRST (1), 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.
378
CAUTION:
{
Shifting the transfer case to NEUTRAL can
cause your vehicle to roll even if the
transmission is in PARK (P) (or, if you have
the manual transmission, even if you are in
gear). 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 PARK (P) (or, put your
manual transmission in FIRST (1)). But do
not shift the transfer case to NEUTRAL.
Leave the transfer case in the Two-Wheel
High, Four-Wheel High or Four-Wheel Low
position.