Oh ok, sounds like the balls or something have gone then. We have found some diff balls seem to be a little below standard recently and the diff goes off very quickly, but leave it a few hours and it feels fine again. Maybe try a rebuild with new balls/washers and thrust race and I would suggest ceramic balls, I have switched to these recently and instead of having to rebuild my diff at least every meeting I can just leave it...which suits me fine
Can't say I have noticed it on mine for the side to side. Have you flipped the rear hangers at all??? if you have you need to shave the pips level with the main block. I know a long time ago the rear towers used to be out on the xx4 and we ran a washer under one side to correct it. Best way to check that is to check the droop is correct side to side front to rear, just put the front on the table and keep it level and raise the rear, if one wheel leaves the ground before the other something is out. Then do it for the front. If it is out check the shock lengths then all other parts to make sure they are seated correctly, especially where you screw up through the rear hangers in to the tower, it is possible the screw has tightened on to the hanger and not pulled the tower right down flush.
E.