Need Help To Get Power Back!!

Hey guys, I have a 88 Formula 350, SES light is on, code 36..heres the deal: When the engine is cold I have full power, but once it warms up to normal operating temperature, if I put more than like 40% throttle it starts stuttering the power and I go nowhere, and if I floor it then I get even less response. But when its cold no problems at all. Any ideas on what it could be?

Sounds like symptoms of a bad catalytic converter to me.