GMC 1997 Safari Owner's Manual page 96

FIRST (1): This position gives you even more power
(but lower fuel economy) than SECOND ( 2 ) . You can
use
it on very steep hills, or in deep snow or mud. If the
selector lever is put in FIRST (l), the transmission
won't shift into first gear until the vehicle is going
slow enough.
I
NOTICE:
If your rear wheels can't rotate, don't try to
drive. This might happen if you were stuck in
very deep sand or mud or were up against a solid
object. You could damage your transmission or
transfer case or both.
Also, if you stop when going uphill, don't hold
your vehicle there with only the accelerator
pedal. This could overheat and damage the
transmission. Use your brakes or shift into
PARK (P) to hold your vehicle in position
on a hill.
Locking Rear Axle
If you have this feature, your rear axle can give you
additional traction on snow, mud, ice, sand or gravel. It
works like a standard axle most of the time, but when
one
of
the rear wheels has no traction and the other does,
the locking feature will allow the wheel with traction to
move the vehicle.
All-Wheel Drive (Option)
If your vehicle has
all-wheel drive, your
engine's driving power
is sent to all four wheels
for extra traction.
This is like four-wheel drive, but there is no separate
lever or switch to engage or disengage the front axle.
It is fully automatic, and adjusts itself as needed for
road conditions.