well, I have had a few EPX Pro models and for the most part never had diff issues.
I did have 1 tornado that started blowing the rear diff, but it was due to a bad bearing.

IMO, if you have to replace a diff, go ahead and get the upgraded one. If your diffs are fine, keep'em.

The upgraded ones are not that much more expensive than the stock ones. The only difference is the metal is harder. So if you have to replace, go ahead and gett'em.