RE: Check the cat......
From another forum...
I have heard that you can check for a plugged cat with a temp/pyro gun. It the temp of the pipe coming out of the cat is much less than the temp of the pipe in front of the cat then you have found the problem.
You can also do a vacuum test...
A normal reading at idle with a gradual drop to 0 or very near it as the engine is speeded up is caused by a choked muffler, clogged cat converter, or any stoppage of exhaust flow.