so i recently put a hyper .21 in my race savy, yes a .21, and i blew my rear diff. when i first bought the truck it had a mach 427 and it blew the front diff, and while replacing it i decided just to switch to x bulkheads. and now i blew the rear diff. is this common, do they just need to be shimmed perfect, what do you guys think about the cen diff mod. Ani input will be helpfull.