Regarding the issue of whether your Cat. Conv. is the cause of your pour running problems.
I experienced a plugged one many, many years ago. In that case, the car didn't run rough or miss, it just lacked power at higher RPM, imagine a smashed flat exhaust pipe. It first raised its ugly head at interstate speeds, even slowing on inclines.
The mechanic diagnosed it by timing about an 1/8 mile out back in a big parking lot first. Lucky thing is it had a bypass (drain) plug in the bottom. So he removed that and repeated the run, noting the difference. Yup, thermal meltdown of the Cat.
Maybe this info will help you troubleshoot your problem.
BTW, one of the guys here suggested I take the MAF out and spray clean the little wires. They sell a cleaner esp. for this sensor and recommend cleaning with every air cleaner change. MUCHO improvement!