Have you ever replaced your O2 sensors? The O2 sensors are the only feedback that you vehicle's engine controller has on the quality of the fuel burn - assuming that everything else is in working order (MAF, injectors, spark plugs/wires), and you can now knock the cats out of the equation since they are new. Not sure if you can get a heading of the O2 voltage or cross-counts from the OBD system - I will likely read rich or lean.
I was talking to a guy the other day when I got my car e-tested, and he mentioned that a few people had passed simply by changing their oil (not sure what the truth to that one is).
You can switch plates on my car and swap in your VIN
.
