Alright I'm going to try and give as much detail as possible so here goes. I have an engine power issue. While vehicle is idle or slower speeds with light accel it seems to function properly. When I accel harder and higher speed the engine power lacks as well as getting what sounds like a vacuum leak when really getting on it. I have no check engine light on nor does it come on when I'm experiencing the lack of engine power. I did note a couple weeks ago that the 3rd cat sounded like the material inside had come loose and rattled. I also get an noticible sound almost like a back feed of air(belch) imediately after shutting off the engine. I'm leaning toward a restricted/clogged cat but any input would be considered.

 

Best to take the oxygen sensors out and put the pressure gauge. With this you can figure out which cat exactly is plugged in, if any.
Maybe autozone will have some for rent.

 

Remove the cat and go for a ride