Chevrolet 2008 Silverado 1500 Pickup Owner's Manual page 38

Lap Belt (Crew and Extended Cab)
This part is only for the lap belt. To learn how to wear a
lap-shoulder belt, see Lap-Shoulder Belt on page 1-28.
You vehicle may have a center seating position.
When you sit in the center front seating position, you
have a lap safety belt, which has no retractor.
To make the belt longer, tilt the latch plate and pull it
along the belt.
1-34
To make the belt shorter, pull its free end as shown
until the belt is snug.
Buckle, position, and release it the same way as the
lap part of a lap-shoulder belt. If the belt is not long
enough, see Safety Belt Extender on page 1-35.
Make sure the release button on the buckle is positioned
so you would be able to unbuckle the safety belt
quickly if necessary.