[Christ]

Clogged/burned cat could cause serious loss of power, overheating, etc..

Disconnect your exhaust before the cat, fire it up, and rev'er up a bit... see if it stops that from happening.

If it does, remove the cat completely, and shine a light through it. You should be able to faintly see light at the other end. Do it in a dark place, so you'll see better. Shake the cat while it's off... if anything rattles, it's bad, unless the rattling noise is just the heat shield.