Engine Eec Fault Codes

So the car's been running fine. Comes time for the Calif smog test. The car's been passing as-is for the last 10-12 years, but now they won't test it due to the BBK H-Pipe since it only has 2 cats, compared to the factory 4 cats. So I take the car to a local muffler shop to have my old factory H-Pipe put back on.

When I first take the car out, it doesn't feel right, way low on power, sluggish, surges at idle. After about 15 minutes I'm climbing a hill to get home and it just doesn't want to go at all. I'm downshifting just trying to keep it moving, any right pedel and it just loses all power. Somewhere in here the CEL comes on. It doesn't stall, but any more than the slightest bit of gas and it won't move. I take 3 miles of side streets in 1st and 2nd and a lot of clutch to get home. Hot and pissed.

I hook up the code reader and get the following:
172 - Heated oxygen sensor fault/lean bank #1
173- Heated exhaust gas oxygen sensor fault/rich bank #1
176 - Heated exhaust gas oxygen sensor fault/lean bank #2
556 - Fuel pump relay primary circuit fault
456 - This code wasn't in my book - google says "Insufficient RPM decrease during test", but I was doing an engine off code read, so not sure about that one.

Any thoughts on the best place to start to figure this out? Don't know what 12 years of sitting in my garage might have done to the cats on the factory H-Pipe. The O2s have been fine up until now.

Thanks.

yes, the same o2 sensors have been working fine in the BBK exhaust for 12 years. Now that they're back in the factory pipe I'm getting codes. It seems unlikely that both would go bad right now, but I have to start somewhere I guess.