Not attacking you at all. I had an open-diff 240 before this one that I have now, and it would snap back out of a turn with my tires being worn. As soon as I got a new set of tires, it felt different. The right rear is the driving wheel. My husband's 240 sometimes acts funny as far as steering goes, but that's only when HICAS kicks in. You've got a '90, so no HICAS there. I'm really not sure what your issue could be...
Change your diff fluid, maybe that might help the engagement be smoother. Or, it may be something steering-related, which I personally don't think it is.