GMC Sierra 2000 Owner's Manual page 256

CAUTION:
Changing a tire can cause an injury. The vehicle
can slip off the jack and roll over you or other
people. You and they could be badly injured.
Find a level place to change your tire. To help
prevent the vehicle from moving:
1. Set the parking brake firmly.
2. Put an automatic transmission shift
lever in PARK (P) or shift a
manual transmission to FIRST (1)
or REVERSE (R).
-
3. If you have a four
be sure the transfer case is in a drive
--
gear not in NEUTRAL (N).
4. Turn off the engine.
To be even more certain the vehicle won't move,
you can put blocks at the front and rear of the
tire farthest away from the one being changed.
That would be the tire on the other side of the
vehicle, at the opposite end.
-
wheel drive vehicle,
The following steps will tell you how to use the jack and
change a tire.
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