Welcome to BonnevilleCLub
I am not to far from you here in the Midland area. If you need any help with the car, let me know, I would be glad to help out
also, it does sound to me like the cat is plugged up, and I have never heard that if the car cools down it would be ok. I have had two cars ( '95 Monte Carlo Z 34 and '91 Saturn SC-2 ) that had the cat plugged up on them and they both would hardly run, didn't matter if they sat overnight or were already running, they had no power.
Have you been hearing any rattling noises from under the car lately? When you lift up the car ( make sure it is on jackstands, of course ) kick the cat and see if it rattles. If it does, that is a dead giveaway that it is junk and will save you some time from taking the exhast off of the manifold. If it doesn't make any noise, I still would suspect the cat though.
On a side note, I recently swapped my exhaust with my parts car ( 1993 SSEi ) and I actually found it easier to get at the bolts from the top of the engine with a couple of wrenches. But, if you have a swivel for your ratchet and some extensions, that would probably be the easier way to go.
after reading your first post carefully a second time, what exactly do you mean by running rough? Do you mean that it just has no power, or it is actually running rough like misfiring?
When was the last time you did a full tune up on the car or at least plugs and wires? As far as the ignition control module being tested, people here have had bad ones test out good and good ones test out bad so the test isn't %100 reliable.