Austin1991

Thanks everyone for all of your great input!
After two months, I finally got around to fix the problem. It turns out that it was the pipes in the Y shape that go from the catalytic converter to the manifold. Something inside them must have collapsed, because if I took the catalytic converter completely off, I could get the car to redline. The actual material inside the catalytic converter looked perfectly clean and in good shape. So, it wasn't the actual catalytic converter....it was the pipes. I hope this will help someone else.

European Parts Direct out of California seemed to have the best price for an OEM catalytic converter.

Thanks again for all of your help.