I recently replaced all 8 plugs in my '01 4.6 with 8 Motorcraft plugs. Got a set of new COP's from Global Automotive. I had some problems, so a mechanic (a trusted one, if you can believe it) said that becuase it had misfired, (I had a miss in #4) that the cats may be clogged. Before I invest any money in a Magnaflow exhaust, I wanted to get some feedback. I just cleaned the IAC and the pickup seems to be back to where it was when I bought the truck. It is not throwing any codes, but still hesitates between 35-45 MPH. Like I said, the HP feels fine. Is there a way I can check the cats without taking it anywhere? Any help is appreciated.