Haven't heard of the pinion problem, little confused on that if its shimmed. I know of the bevel gears but I have the same type of problem in my lst2, plus I snap pins in the trans, and in the diffs, but yet again I'm running brushless and I'm kind of hard on it, and before you say something about my slipper, its set fine, maybe a little loose. if you change the all the gears in the diff with hot bodies, it pretty much solves the issue if shimmed, I know the pins are kind of weak, but that seems kind of common for both.
Whats wrong with the cups?
Not arguing, just getting what you think.
By the way, checking out your lst builds, they're pretty sweet.