yup i had the same issue, try banging the cat with a rubber mallet or something made of plastic and listen for stuff rattling around inside there. If you hear rattling most likely chunks of the cat element have broken off and it needs to be replaced.If you have a Cat. Conv. that could be your problem. When they're clogged you have a loss of high end power, and sometimes there are no other symptoms. Seems like your exhaust is due for some maintenance. I replaced mine in my 89 4.2 and now I have all the power I need. Before I couldn't get it to go up a hill.