go to your GM dealer and buy at least four. keep two in the truck at all times.
I don't care HOW you install them, THEY WILL EVENTUALLY FALL OUT.
If you are lucky, they just fell out. IE, they didn't BREAK AND THEN FALL OUT.
Before just sticking a new set of bolts into those holes, use a flashlight to make SURE that you don't have a broken bolt still in the hole.
If you do, you will need to carefully pick it out. THEN replace the bolts.
GM bolts are about $5 each and they stretch just a little so they last a little longer than a standard grade 8 bolt.