Marcperdue questioned: "Also, if the cat were blocked, wouldn't I NOT have 
exhaust gases coming out the tailpipe?"� 

Depends on how much it is plocked.  It is fairly easy to disconnect the 
exhaust pipe from the cat and muffler and run it straight out.  It is a 
little loud, well, a lot loud, but that test should eliminate the plugged cat 
question.  You can also look into the cat and see what it looks like.  
Shouldn't be carboned or melted or broken up.  Just a lot of tiny holes.