Got a 93' 302 V8, and I've had the trans replaced twice now and it still blows out around 6-10K miles. Its around that point now and it's started slipping (I think) in 2nd, going up to 3rd or when given some gas, like up a hill. But it's gotten ALOT worse since I unbolted my cat back so it's just coming right out from the Y. Friend said maybe it's running lean/rich, another said try slip-fix in the trans, I'm crying cause I might have to put ANOTHER trans in it. Any ideas?

The shaking is intense too, like you can see the RPM's stutter and not keep accelerating and it's quite a cringe worthy stutter.

 

Have you checked the fluid level? Sounds like the fluid is low and you burn them up.

 

I have had a Jasper transmission installed on my other truck. They upgrade components that are know for its weakness to give it a higher reliability. It requires a Jasper authorized installer and a transmission cooler. If you do the install on your own I am not sure if they will give you a warranty.

 

A; dumping your exhaust right at the Y is probably heating up your trans fluid A LOT which is not good, the oilpan is supposed to help cool it, and
B; your O2 sensor can't be working properly with the pipes cut off that close to it which would totally mess with your computer inputs which could mess with the signal it sends to your trans, and
C; if it seems like all this is happening since you cut your exhaust off, see A and B.