GMC C series 2002 Owner's Manual page 63

Two Speed Rear Axle Electric Shift
-
Control (If Equipped)
If your vehicle is equipped with this feature, you'll find
a label on the headliner above the windshield or in
another place near the driver that show how to use it. Be
sure to follow the directions carefully. Use the following
directions based on the type of shift control you have.
Automatic Transmission
2-20
The knob for the rear axle
shift control is located on
the shift tower to the right
of the shift lever.
When the knob is up, the rear axle is in the high range.
Push it down to get the low range.
-
The two speed axle should be in low range when you
park the vehicle. Apply the parking brake, shift to
PARK (P) or NEUTRAL (N) and shut off the engine.
-
To operate off road or under a heavy load, shift into low
range when the vehicle is standing still and then operate
the transmission normally.
On the highway, with the axle in low range and
transmission in top gear, you may shift the axle to high
range by raising the switch and releasing the accelerator
momentarily. Reapply the accelerator after you shift.
Under light load conditions, first shift the axle into the
high range with the vehicle at a standstill and then
operate the transmission normally.