GMC 1996 Sonoma Owner's Manual page 183

rking on Hills
I O U
really should not park your vehicle, with a trailer
attached, on a hill. If something goes wrong, your rig
could start to move. People can be injured, and both
your vehicle and the trailer can be damaged.
But if you ever have to park your rig
on
a hill, here's
how to do it:
1.
2.
3.
4.
5 .
6.
Apply your regular brakes, but don't shift int.0
PARK (P) yet, or into gear for a manual
transmission. When parking uphill, turn your
wheels away from the curb. When parking downhill,
turn your wheels into the curb.
Have someone place chocks under the trailer wheels.
When the wheel chocks are in place, release the
regular brakes until the chocks absorb the load.
Reapply the regular brakes. Then apply your
parking brake, and then shift into PARK (P), or
REVERSE (R) for a manual transmission.
If you have a four-wheel-drive vehicle with a
manual transfer case shift lever, be sure the transfer
case is in a drive gear -- not in NEUTRAL (N).
Release the regular brakes.
It can be 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.
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, use the steps
that follow.
If you have four-wheel drive with a manual
transfer case shift lever and your transfer case is
in NEUTRAL (N), your vehicle will be free to
roll, even if your shift lever is in
PARK (P). So,
be
sure the transfer case is in
a
drive gear
--
not in
NEUTRAL (N).