GMC Sierra 2000 Owner's Manual page 55

If you need to have an anchor installed, your dealer can
obtain a kit with anchor hardware and installation
instructions specifically designed for this vehicle.
The dealer can then install the anchor for you. This work
will be done for you free of charge. Or, you may install
the anchor yourself using the instructions provided in
the kit.
Securing a Child Restraint in a Rear
Outside Seat Position (Extended Cab)
1-42
If you have a Crew Cab, see "Securing a Child Restraint
in a Rear Outside Seat Position (Crew Cab)" later in
this section.
-
You'll be using the lap shoulder belt. See the earlier part
about the top strap if the child restraint has one. Be sure
to follow the instructions that came with the child
restraint. Secure the child in the child restraint when and
as the instructions say.
1. Put the restraint on the seat.
2. Pick up the latch plate, and run the lap and shoulder
portions of the vehicle's safety belt through or
around the restraint. The child restraint instructions
will show you how.