Limping home mode but never stalls

For over 2 years, but much more frequently and lenghtier recently, my 2000 Chevy Prizm, with a used 07 Corolla engine with 75,000 mile on it now, has seemed like it wants to die but then will eventually kick in and you would never know anything had happened.

Started out as a maybe 50 yard slowing down but is now up to about a quarter mile with some occasional noise like misfiring on the last two times it acted up.

Have had it in to a couple of mechanics and no one can seem to determine what it is. Had a mass air flow sensor put in about a year ago and was told if that doesn’t fix it I would need a catalytic converter (shows up in engine codes) but second mechanic told me my problems would not be the result of a bad catalytic converter. If that was it, the car would die not keep on going.

Will I just have to wait for it to die for someone to figure out my problem.

It doesn’t have to die for the cat to be a problem. You obviously need to find a tech that can test exhaust backpressure. That’s the only way to be sure and from your description, a likely culprit. Of course it could also be a fuel filter which is a maintenance item anyway.