Hold it, Hold it, HOLD IT!!!!
Check your Catalytic Converters. I was a happy camper for a little while until the cat on my 95 'stique became blocked. All of a sudden, I couldn't get beyond 75mph. It became worse and worse until 55mph became a challenge. Eventually,one of the hoses on the DPFT (or I think those are the letters) popped off due to back pressure.
Since I've replace the whole exhaust, I've been happy again.
Got a SVT dual on there now.
Good Luck.
PS: it's easy to see if the IMRC is working right, just start it up and shine a flashlight down there. You'll see it work by massaging the throttle.
