I agree on swapping the sensors front to back. The fact that once you clear the engine of excess fuel it drives OK would indicate it's being flooded. The flooding is leading to fouled plugs causing the misfire.
Swap the sensors front to back. I would like to know what you have for fuel pressure. Have you checked for vac leaks? Have you tried cleaning the MAF? How does it run when started cold?
Ah, you posted while I was typing.
You can hear gas being burned in the cats? There are only a few things that can cause this, firing order, injector stuck wide open, or stuck valves.
SHUT IT DOWN! Check firing order, fuel pressure, and compression test, ASAP!