Air Suspension - GMC 2003 GMT560 T-Series Owner's Manual

Automatic Transmission
When the switch 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.
The switch is located on
the instrument panel to the
right of the climate
controls.
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 rear axle in low range and the
transmission in top gear, you may shift the rear 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 rear axle into
the high range with the vehicle at a standstill and
then operate the transmission normally.

Air Suspension

Your vehicle may have air suspension which is designed
for a single-axle on-highway use.
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