Highway Screamer!

[UltraBlue71]

I am 6 months into my build and finally cresting the hill on the downward slide, finally started some painting last night!
Its a 3/4t with a dana 60 reaend, and the saginaw 4spd top loader shes geared so low I just use 3rd and 4th, I can start out from stoplights in 3rd!Friends riding with me think its hilarous that I have a 2 speed (Low and high). So needless to say it screams at 65-70 mph 3200rpm, My question is should i get a new rearend or swap trannys or both, I dont really want an auto, I think a 5 speed would be cool, and I read a few of the S-10 tranny swap threads, but I just dont know if they will hold up. I eventually want to rebuild my stock 350 crate motor to 350-400 HP, any suggestions???