o2 or cat... what to do?

I'm pimpin a 98 SS with 35k. Weird thing have been happening. The car sometimes almost stalls when I thomp on it or gwet on the highway. I give it gas and it's like nothing happens. If I let up on the throttle for a sec then maintain my speed things are fine until I give it more gas. I'm throwing O2 codes for all 4 sensors (low voltage.) But the SES light will go off on it's own if I drive sensibly arounf town for an hour or two.

Do you think it's possible all my o2s crapped out or could I have a Cat problem? All this started when I put a new muffler on a few weeks ago. Could a leak in the exaust cause this.

Help, It's no fun not being able thomp on it when ricers drive by.

I'd start with the simple stuff. A complete tune up. Plugs, wires, air filter, fuel filter, PCV valve, clean the MAF. Then see what it does.

Oh and try taking the smooth bellow out and using the stock one. I've heard of some thinner ones sucking closed and choking the engine out.