[89IROC&RS]

yeah, sounds to me like crappy workmanship, if a rear end is set up properly than you shouldnt be having these problems, for the pinion to actually come out from the housing the bolt holding it in place would have to come loose, or not been proporly torqued to begin with, inproper contact pattern and backlash settings would create all the problems your talking about. the stock rear end should handle 4.10 gears and 285hp just fine. take it to someone who knows what they are doing.