GMC SIERRA 2020 Owner's Manual page 93

92 Seats and Restraints
When installing a child restraint with
a top tether, you must also use
either the lower anchors or the seat
belts to properly secure the child
restraint. A child restraint must
never be installed using only the top
tether.
For a forward-facing 5-pt harness
child restraint where the combined
weight of the child and restraint are
up to 29.5 kg (65 lb), use either the
lower LATCH anchorages with the
top tether anchorage, or the seat
belt with the top tether anchorage.
Where the combined weight of the
child and restraint are greater than
29.5 kg (65 lb), use the seat belt with
the top tether anchorage only.