GMC SIERRA 2020 Owner's Manual page 97

96 Seats and Restraints
Regular Cab Driver Side Anchor and Loop Center Anchor and Loop (Double
(Double and Crew Cab) and Crew Cab)
For regular cab models, the top
tether anchors are on the back
panel behind the passenger seat(s)
or center seat. Be sure to use an
anchor directly behind the seating
position where the child restraint will
be placed.