Check Engine Light Help..

I just purchased a 97 4.0 and need a bit of help. I went to get it NY inspected and it failed for a bad oxygen sensor on Bank 1. I replaced them and the check engine light came back on. It was then suggested that the culprit might be bad catalytic converters as they were not the correct ones, so I replaced those. The mechanic went to re set the check engine light and found no codes as well as it indicating that the light was not on..Yet the light was still on and the computer said that it was not, so we hooked it up again to get it to pass and it failed the inspection again..I am thinking about a getting a Chevy...Any ideas ?:confused:
Thanks