Thanks for the reply's gang, but.....
It hasn't slipped in over a week. My buddy found a tranny in his yard at work, so I will probably grab that regardless, as I will need it one day and I can get if for cheap. And if time permits, I would give it an overhaul before it gets installed.
I have some goofy driveline vibrations, so I'm leaning more towards that as the problem rather than the trans.