GMC 2005 Yukon Owner's Manual page 27

If the seatback cannot fold flat because it interferes with
the cushion, try moving the front seat forward and/or
bringing the front seatback more upright.
Once the seatbacks are folded down, the rear seat
footwell area will be exposed and will have to be
covered by the load floor panel. To create a load floor,
do the following:
2. Pull the seatback
release lever up and
pull the seatback
forward. Then fold it
until it is flat.
1. Release the panels from the seatbacks by pushing
forward on the latches.
2. Then fold the panels back to cover the rear seat
footwell area.
If you have removed the head restraints to fold the rear
bucket seat, be sure to reinstall them on the seatback
after it has been returned to the normal seating position.
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