GMC 2006 Yukon XL Owner's Manual page 12

Reclining Seatbacks
CAUTION:
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If the seatback is not locked, it could move
forward in a sudden stop or crash. That could
cause injury to the person sitting there.
Always push and pull on the seatback to be
sure it is locked.
To adjust the seatback, lift the manual lever located
on the outboard side of the seat. Release the
lever to lock the seatback in the desired position.
1-6
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.