So what assortment of Torx bits will I need to fix things on my '99?

I already got 1 for the bed (T55?)
Now I need to adjust the tailgate striker, what size is that?
What else will I need a Torx for? I have the small screwdriver bit sizes t10 - t40

 

I suggest purchasing a set of Torx sockets that way you've got all at your disposal rather than buying one by one. I got mine from Ace Hardware and it wasn't expensive ($20?)...came with like 8 or 9 sockets ranging from T10 to T60.

These trucks have them scattered from tailgate strikers to seat belts to seats to bed bolts to front axle straps, etc. There's even a set of EXTERNAL TORX holding your flywheel to the crankshaft.