So tonight I was driving home on 275. When i was in 5th gear at about 3000 rpm and punch it the tranny or diff will start to slip but I'm unsure on what is slipping. I tried it in 4th, 3rd and 2nd and it does the same thing. So pretty much I can't punch it anymore without having to slow down & then gradually taking off. Please help because I'm starting to think it's my diff going bad but I'm not sure. I have a NA-T with aem series 2 with 440 injectors and bc racing coilovers.

 

Sounds like your clutch, also you shouldn't "punch it" in 5th gear if your using a w58. I remember reading a post not to long ago where another NA-T sc was trying to pass somebody on the highway and ended up blowing up his transmission.

But anyway to circle back sounds like the clutch, the differentials are pretty hard to break from what I'v read.