GMC Sonoma 2001 Owner's Manual page 60

In Canada, the law requires that forward
restraints have a top strap, and that the strap be
anchored. In the United States, some child restraints also
have a top strap. If your child restraint has a top strap, it
should be anchored.
Anchor the top strap to this bracket (regular or extended
cab). Once you have the top strap anchored, you'll be
ready to secure the child restraint.
1-46
-
facing child
The three anchor points for the rear seat child restraint
positions in the Crew Cab are located on the back wall
behind the rear passenger's seat.
Anchor the top strap to one of these anchor points.
Be sure to use an anchor point located on the same side
of the vehicle as the seating position where the child
restraint will be placed.