Chevrolet 2008 Tahoe Owner's Manual page 54

To make the belt shorter, pull its free end as shown
until the belt is snug.
If the belt is not long enough, see Safety Belt Extender
on page 1-50.
Make sure the release button on the buckle is positioned
so you would be able to unbuckle the safety belt
quickly if necessary.
If you find that the latch plate will not go fully into the
buckle, see if you are using the correct buckle. Be sure
that the latch plate clicks when inserted into the buckle.
1-50
Safety Belt Extender
If the vehicle's safety belt will fasten around you,
you should use it.
But if a safety belt is not long enough, your
dealer/retailer will order you an extender. When you go
in to order it, take the heaviest coat you will wear,
so the extender will be long enough for you. To help
avoid personal injury, do not let someone else use
it, and use it only for the seat it is made to fit.
The extender has been designed for adults. Never use
it for securing child seats. To wear it, attach it to the
regular safety belt. For more information, see the
instruction sheet that comes with the extender.