Red-Ford

So between 3rd and 4th gear, something stutters, not all the time, but up hill seams to provoke it, although it happens randomly when going in between the gears. When it stutters, think of a Mexican rolling their r's for a second, it sounds exactly like that.

Praying to god it is my back end, I had a guy open my diff and come to find the spyder gear needs to be replaced. When I replace it, will this solve my problem? Or is it a trans. problem?

This is on a 1997 F-150 XLT 4x4 4.6L V8, automatic transmission