GMC 2006 Envoy Owner's Manual page 53

For seven-passenger vehicles, the top tether anchors
for each seating position in the second row are located
at the bottom rear of the seat cushion. Be sure to
use an anchor located on the same side of the vehicle
as the seating position where the child restraint will
be placed.
Do not secure a child restraint in the right front
passenger's position or in the third row seating position,
if your vehicle has one, if a national or local law
requires that the top tether be attached, or if the
instructions that come with the child restraint say that
the top tether must be attached. There is no place
to attach the top tether in this position.
Accident statistics show that children are safer if they
are restrained in the rear rather than the front seat. See
Where to Put the Restraint on page 1-42 for additional
information.
Seven-Passenger Vehicles
1-47