Like GTSHOLgi said you have to break them in, change the fluid, then do your racing. I have 3:55s and a bit more than 550 and so far so good.
Remember: No spirited driving for the first 500 miles! Otherwise, your new gears will not last for long
I'm actually buying them used from a member on here that only had 6,000 miles on it so I can spirit drive it as soon as I leave the shop he he
I have roughly 550hp.