Actually the owner's manual might not help too much. It mostly covers generic type things.
Inside the glove box, there will be a bunch of 3 character codes on a sticker like label:
You're looking specifically for
MT1 or MT5 (that is the 4L80e transmission code for either a 6.0L or an 8.1L)
LQ4 or LQ8 (6.0L engine or 8.1L engine)
G80 (Locking differential)
Z82 (Trailer package)
GT4 or GT5 (3.73 or 4.10 gears)
My fav would be MT1, LQ4 (better fuel economy- less power than LQ8), G80, Z82 and GT5.
If you see these codes on the sticker in the glove box, you should be in good shape. If you have none, then I would say you might need to modify the truck a bit and/or consider a different truck if it has the 5.3L engine.
Hope this helps a bit.