By gutting the main cat you opened up a giant opening in the exaust system so you lose gas momentum as soon as it hits that open chamber. The quick fix is to get a piece of pipe that will slide inside the cat and weld that into place.
From the sounds of it, your manifold cats are the ones that are clogged and causing the power loss. You need to gut them or replace them. I would not recommend gutting them on the car though as any open exhaust valve potentially lets those particles into the engine.
I off manifold gutting as a service if you want to send them to me. Just drop me a PM or email. I usually offer a core exchange service but I don't have any 95 cores.
Thanks,
Rick
