[GMC70c20]

which 12 bolt are you talking about? The ones they put in cars or trucks. The ones they put in trucks are pretty week even with axles and a new carrier. Now the 8.875" 12 bolt (the one they put in cars) with a good set of axles and a good carrier then ya it should handle 400-500hp hooked. Like cableguy0 said you could put a tired 10 bolt under it and hook 1000hp to it but if it never hooks itle never break. Another thing to remember is the more weight you are moving the more stress it puts on drivline components so maybe instead of spening $600 on a carrier tryd to shed 300-400 lbs plus then it will hook better and drive better. Or do get a new carrier and still try to shed some weight.