GMC 2007 Sierra - Manual (Page 63)

For crew cab models, there are covered top tether
anchors for each seating position located on the
back panel of your vehicle, behind the rear
seat. Remove the trim covers to access the
anchors.
Do not secure a child restraint in the front
passenger’s position if your vehicle has rear seats,
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 55
for additional information.
Crew Cab
63