GMC Chevrolet Tahoe 2003 Manual page 12

Reclining Seatbacks
1-6
To adjust the front seatback, lift the manual lever
located on the outboard side of the seat. Release the
lever to lock the seatback where you want it. Lift
the lever again without pushing on the seatback and the
seatback will go to an upright position.
If your vehicle has power seats with a power recliner,
see Power Seats on page 1-4 for further information on
how to operate the reclining seatback feature.