GMC Yukon Denali 2003 Owner's Manual page 29

On the Yukon XL Denali models, you must first remove
the headrest and store it on the top of the seat
cushion as shown next. Yukon Denali lever shown,
Yukon XL Denali similar.
2. Pull the seatback
release lever upward
and pull the seatback
up and fold it down until
it is flat.
Pull the headrest out from the seatback and slide the
pins into the holes provided in the top of the seat
cushion.
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.
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