GMC 2010 T-Series Owner's Manual page 8

Reclining Seatbacks
WARNING:
You can lose control of the vehicle if you try to
adjust a manual driver's seat while the vehicle is
moving. The sudden movement could startle and
confuse you, or make you push a pedal when you
do not want to. Adjust the driver's seat only when
the vehicle is not moving.
1-4
To tilt the seatback, turn the reclining knob. The knob is
located on the outboard side of both seats.