OK so i have been gettin a hissin noise only under acceleration, I thinking its only a busted cat or exhaust leak blow it off. Then, while driving home hard accelaration in second gear and the car shut off completely. I quickly put it in neutral cranked it on the fly and stayed out of boost the whole way home. The car seems to have lost a lil power lately as well, any ideas? maybe a line off somewhere or something?

 

Probably a bad cat...

 

that was my first assumption. The car has gotten louder, but it wont do the hissing noise unless i boost. I can rev it in neutral and nothing happens, sounds completely normal

 

Try getting on it a little and watching the gauge. If you notice higher than normal boost(or very slow rise to full boost) check the cat.

 

Boost/vacuum leak??

 

Most likely your cat and your bypass valve is open. Trust me at our dyno meet today I had the same thing and because of it only put down 150 on the dyno sucks ass i'm takin it to the dealership monday bc the cat is still uner warranty