GMC Sierra Denali 2006 Owner's Manual page 51

4. Pull the rest of the shoulder belt all the way out of 5. To tighten the belt, push down on the child restraint,
the retractor to set the lock. pull the shoulder portion of the belt to tighten the
lap portion of the belt and feed the shoulder
belt back into the retractor. If you are using a
forward-facing child restraint, you may find it helpful
to use your knee to push down on the child
restraint as you tighten the belt.
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