GMC YUKON 2018 Owner's Manual page 111

110 Seats and Restraints
If the position you are
using has an adjustable
headrest or head restraint
and you are using a
single tether, raise the
headrest or head restraint
and route the tether
under the headrest or
head restraint and in
between the headrest or
head restraint posts.
If the position you are
using has a fixed
headrest or head restraint
and you are using a
single tether, route the
tether around the inboard
or outboard side of the
headrest or head
restraint.
If the position you are
using has a fixed or an
adjustable head restraint
and you are using a dual
tether, route the tether
around the head restraint.
3. Before placing a child in the
child restraint, make sure it is
securely held in place. To
check, grasp the child restraint
at the LATCH path and attempt
to move it side to side and
back and forth. There should
be no more than 2.5 cm (1 in) of
movement, for proper
installation.