GMC Chevrolet Tahoe 2003 Manual page 122

Automatic Transmission Operation
There are several different positions for your shift lever.
Your vehicle is equipped with an automatic transmission
and features an electronic shift position indicator
within the instrument panel cluster. This display must be
powered anytime the shift lever is capable of being
moved out of PARK (P).
PARK (P): This position locks your rear wheels. It's the
best position to use when you start your engine
because your vehicle can't move easily.
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CAUTION:
It is dangerous to get out of your vehicle if the
shift lever is not fully in PARK (P) with the
parking brake firmly set. Your vehicle can roll.
Do not 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 will not move, even when
you are 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 are pulling a trailer, see "Towing
a Trailer" in the Index.