there are only three sizes of dog bones for the truck, you want the longest (about 4 inchs, don't have my manual)
the other two sizes run from the trans to both diffs

the only time I had any fly out on me is when jumping, when you raise the arm all the way up, there can be just enough flex to let one fly out...or landing wide open throttle can snap one...

Ebay is the way to stock up on parts...