GMC 2010 T-Series Owner's Manual page 9

WARNING:
Sitting in a reclined position when your vehicle is
in motion can be dangerous. Even if you buckle
up, your safety belts cannot do their job when you
are reclined like this.
The shoulder belt cannot do its job. In a crash,
you could go into it, receiving neck or other
injuries.
The lap belt cannot do its job either. In a crash the
belt could go up over your abdomen. The belt
forces would be there, not at your pelvic bones.
This could cause serious internal injuries.
For proper protection when the vehicle is in
motion, have the seatback upright. Then sit well
back in the seat and wear your safety belt
properly.
Do not have a seatback reclined if the vehicle is
moving.
Air Suspension Seats
Your vehicle may have an air suspension seat.
There are two ways you can adjust the seat.
Height Adjustment
Pull the lever up to raise the seat. Push the lever down
to lower the seat.
The height adjustment
is controlled by the air
suspension valve. The
lever for the valve is
located on the outboard
side of the driver's seat.
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