GMC 2005 Envoy Owner's Manual page 49

Seven-passenger Vehicles
For seven-passenger vehicles, there is a top strap
anchor for each seating position in the second row.
The anchors are located at the bottom rear of the
seat cushion.
Do not secure a child restraint in the right front
passenger's position or in the third row seating positions
(if equipped) if a national or local law requires that the
top strap be anchored, or if the instructions that
come with the child restraint say that the top strap must
be anchored. There is no place to anchor the top
strap in these positions.
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