Like everyone has been saying, it's your open diff. I would always try to clutch kick before I welded my diff and all it did was make noise. I welded the diff, and it was a total night and day difference. WIth the open diff I couldn't do anything, then I did a low speed clutch kick with the welded diff a few days after I put it in and the rear end slid out like butter. You've basically solved your own problem by welding the diff, you shouldn't have issues any more. Hope this helped
