GMC 2007 Sierra 1500 Pickup Owner's Manual page 68

2.2. When using a child restraint with a top
tether in the rear passenger position,
raise the head restraint and route
the top tether through the fabric loop.
Then, attach the top tether to the metal
anchor point at the center rear
seating position.
2.3. When using a child restraint with a top
tether in the rear center position, route
the top tether through the fabric
loop. Then, raise the head restraint on
the passenger side and attach the
top tether to the metal anchor point
located at the rear passenger position.
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2.4. Tighten the top tether when and as the
child restraint manufacturer's
instructions say.
3. Push and pull the child restraint in different
directions to be sure it is secure.