beloved Previa sputtering

Hey y'all,

Desperately need some help. My beloved 91 Previa has had an EGR check engine code (71) for awhile now. The symptom is intermittent, usually a sputtering engine (like a gocart) with loss of power. Usually I pull over and rev the engine a bit, or in extreme cases shut the engine off and sit for awhile, and it'll go away eventually. But the problem was getting progressively worse, and when I pulled over I could smell something, and the catalytic converter was extremely hot.

So far I've replaced the vacuum hoses, replaced the vacuum modulator, cleaned out the vacuum solenoid, replaced the actual EGR valve, to no effect. The mechanic says he sees a lot of carbon buildup and cleans that out before clearing the code, handing me the keys, and asking if that'll work. I've had two catalytic converters crack and then rattle, occasionally contributing to my problem by blocking the exhaust.

Any ideas or experience out there? I love this van and don't want her to go before her time! Only 150,000 miles.

Grateful for any input, thanks!