GMC 1997 Safari Owner's Manual page 94

Don't leave your vehicle when the engine is
running unless you have to. If you have left the
engine running, the vehicle can move suddenly.
You or others could be injured. To be sure your
vehicle won't move, even when you're on fairly
level ground, always set your parking brake and
move the shift lever to PARK (P).
See "Shifting Into PARK (P)" in the Index. If
you're pulling a trailer, see "Towing a Trailer''
in the Index.
Ensure the shift lever is fully in PARK (P)
before starting the engine. Your vehicle has a
brake-transmission shift interlock. You have to fully
apply your regular brakes before you can shift from
PARK
(P) when the ignition key is in the RUN position.
If you cannot shift out of PARK (P), ease pressure on
the shift lever
--
push the shift lever all the way into
PARK (P) as you maintain brake application. Then
move the shift lever into the gear you wish. See
"Shifting Out of PARK (P)" in this section.
REVERSE
(R):
Use this gear to back up.
NOTICE:
Shifting to REVERSE (R) while your vehicle is
moving forward could damage your
transmission. Shift to REVERSE
(R)
only after
your vehicle is stopped.
To rock your vehicle back and forth to get out of snow,
ice or sand without damaging your transmission, see
"Stuck: In Sand, Mud, Ice or Snow" in the Index.