Thats Fords awesome limited slip for ya.... my truck did the same thing until I had gears put in it and had them put more clutches in it. I read somewhere that most trucks come with only 3 clutches in it instead of the 5 they should have. If your truck is under warranty I'd take it in to Ford and complain that your limited slip doesn't work the way it should. Also if they redo it for you make sure they put extra 2 in for you.