Poor performance after headers & cat

I installed headers, ORY, and a Rumbler exhaust on my car all at the same time. After about a week, the car started acting very badly. When I go fast, the car almost feels like its getting power cut to it; like when you hit the governor in the car and it cuts spark. Sometimes it will even backfire. My initial thought was the lack of backpressure in the car now because it’s obviously lacking cats and a muffler. But I can’t understand why it took a week for this problem to start occurring after the install.
What’s the opinion, do you guys think it’s related to the new system, or some other problem that just happened to of surfaced around the same time? The fuel filter is new, and I run injector cleaner in it regularly if that helps. What else could it be and what would be the fix?

Thanks everyone.

Check the spark plug wires. One could have burnt on the header.

have you re-torqued all the header bolts? could be getting a nasty exhaust leak...throwing the o2 readings off

i would go through and recheck everything...plugs, wires and all bolts

Hmm, none of the wires seem to be burnt, and the headers don't look at all detached. Is it possible these things can be messed up unbeknownst to the naked eye?

um...yeah...the bolts only have to be backed off a small degree to "unseal" the gasket sometimes...you'd never see it...:think: you should hear it though.

just trust me and recheck everything.

check your wires thoroughly, its a good chance that its a wire....it took about a week for my car to show signs of burned wires if that helps