I'm really getting irritated with this 8t. I should have bought it new......

Anyway, after fixing alot of issues, I've run into one that I cannot seem to figure out. I was running it around the yard a couple of days ago and all of a sudden, it started making a clicking noise from the rear. I figured I blew the diff, so I disassembled the entire truck and cleaned everything and put it all back together. When I took the rear diff apart, there was nothing obviously wrong. No internal diff gears broken or chipped, bearing fair, etc. It seems like the pinion is slipping on the ring gear. There are a couple of chips out of the ring gear, pinion is good. So, I shimmed the pinion gear 0.5mm forward to try to get it to mate better with the ring. It still slips. I'm not sure where to go at this point short of replacing the entire rear end. Any suggestions? TIA.