Remains of old cat inside the backpipe/muffler causing power loss?

After I purchased my 8, 06 Mt 105000 miles, I tuned it up and eventually discovered the cat was clogged. From the manifold side the honeycomb was perfectly intact but when I took a probe into the o2 hole everything was a crumbled mess. So I got a new cat and a few months later the whole cat is bright red after a hard run. I tested ignition, cleaned ess, cleaned spark plugs(which had just a bit of carbon on em) new maf yet high rpm loss is still there. Ssv moves freely and works fine cause I did the shut down test. I also remember after I got the new cat it improved power just a bit. I've ruled out compression since it starts hot Everytime and the motor pulled hard as f*** when it had full power. It sounds like it can't breathe in high rpms and the rpms climb very slow.
So could it be possible I have pieces of the old cat in the catback? Help a fellow rotary brother out?
Thanks

Remains of old cat inside the backpipe/muffler causing power loss?