Pontiac 1998 Trans Sport Owner's Manual page 20

Adjusting the Third Row Solid Bench Seat
There are two levers to adjust the seat forward or
rearward. They are below the center position of the
bench, one in front and one in back of the seat.
Lift up either lever and slide the seat
forward
to allow
for extra storage behind the seat, or slide the seat back to
allow extra room for third row passengers. Release the
lever. Push and pull on the seat to be sure it is locked
into place.
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