Ill almost guarantee that you need to replace the diff cup as well, plastic will do, but since the alums are all over the place, they make a much better replacement.

Here is what happens. If you pull your diff out, and take all the gears out, now clean it up from all the diff oil. You see where the 2 shafts slide into the cup. if you look at all of them you will see where the shaft has carved a groove out of the slot on the plastic cup. Normally its only in one of the 4 slots, however iv seen it worse. This is soemthing i always have to look at when doing a rebuild.

I would most certainly check that next. Because you put a new set of 4 bevels in there, and the first time you you put force on it, the shaft moves into the grove and the mesh is now off, and BAM diff is blown.
I see it quite often on savages and anything that uses that same style (to many to list).

Also note that braking puts alot of force on the diffs, they are actualy what is stoping the truck, becuase the disc's are location on the driveshaft, so the drivtrain takes alot of abuse when stopping. Which is yet another reason to go to the alum cups.