GMC 2001 Denali Owner's Manual page 21

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, on Denali XL
models only, the rear seat footwell area will be exposed
and will have to be covered by the load floor panel(s).
To create a load floor, do the following:
1-8
On the passenger side
of Denali XL models,
the lever at the base
of the seat must be
pushed down to
release the seatback.
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.