GMC 2008 Yukon Denali Owner's Manual page 71

If the position you are
using does not have a
headrest or head restraint
and you are using a
single tether, route the
tether over the seatback.
If the position you are
using does not have a
headrest or head restraint
and you are using a
dual tether, route the tether
over the seatback.
3. Push and pull the child restraint in different
directions to be sure it is secure.
If the position you are
using has an adjustable
headrest or head restraint
and you are using a
dual tether, route the tether
around the headrest or
head restraint.
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.
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