Mine has always had the other wheel to follow just a little after adjustment. You would have to be really low i mean really low on that diff fluid with some hard riding to have the kind of issue your shooting for. I still think you have axel or axels issue! There hard to pinpoint when its coming from them.
Question, have you drained the diff fluid to see what it looks like as in any harsh discoloration or debris in it? Id bottle it in a clear container when u do it and keep it just in case for testing. Either way, it wont hurt to do and wont cost u much to put new fluid in it . Without seeing it physically, my money is on axels