Thanks everyone for the help, PROBLEM SOLVED! It ended up being the cat clogged just as fc735 said. As far as the detonation goes, I DO know what it sounds like, and it was definately detonating...why the cat caused this I don't know. She runs perfectly with no exhaust.

In reply to 1.8T3t04e, I realize that the autometer guage is not all that acurate, but it can give you a general idea as to whether you're running PIG RICH or DEADLY LEAN, and that's all I was saying. Thanks for your suggestions, I'm still going to make sure all my valves are OK even though everything seems to be operating smoothly.

I really appreciate everyones suggestions and help. Thank you all.