Hey drifter420, the Gumout Regane might have helped. If it cleaned up carbon on the exhaust valves it could help them seal better. It's hard to say exactly what it might have done to the cat; maybe it helped.
One other thing that bears mention is that a plugged muffler or tail pipe could cause the same symptoms as a plugged cat.
"I believe the cat is clogged then.. I have used a Laser Temp gun before and it's cooler behind the cat then the front."
That sounds like a bad cat. You might want to retest you catalytic converter with the Laser Temp gun after 15 minutes of spirited driving, including some hard acceleration. You want to make sure that cat has a chance to light up. Oh, and one drivability symptom of a plugged cat is that then engine bogs down under load, like hard acceleration or climbing a hill.
"My mechanic did check the readings on the rear 02 sensor ( after cat ) and it doesn't move.. no voltage fluctuation
(the front does ) so he's saying either my cat is dead or the rear 02 sensor is gone."
I'm not sure what your mechanic is saying, but on the face of it he appears to be dead wrong
. If you were take a lab scope and look at a good
catalytic converter, the front sensor should show a lot of activity switching from high to low, while the rear sensor should look like it was a "flatliner". The rear sensor should have a relatively flat output with little fluctuation. I suppose if the cat was completely plugged, then maybe you'd get a flat line too.
A lot of voltage fluctuation on the rear O2 sensor means that the converter is not
working efficiently. It is far less common for the rear O2 sensor to go bad compared to the front one.
If your brother is a good sport, and has a compression gauge, you might want to ask him to do a compression check on all the cylinders. It could help you spot a burned or leaking valve.
Also with the vacuum gauge you should have him quickly
raise the RPMs to about 2000 RPM. Hold it there and watch the needle. If it drops to a low reading and is slow to climb back up, then you might have a restricted exhaust, either a plugged cat or muffler. At plain idle you should have about 17 to 20 inHg of steady vacuum on a good engine.
It would help us if you supplied some more information, such as year, make, model, engine size, pertinent history of the vehicle. Keep us posted. Good luck.