I should of asked to what did autozone check. Is the check engine light on and autozone read the codes?
Clogged cat could be a problem (that would be some high milage) put your hand over the muffler output (do this cold then start car or it will be HOT) there should be some force and it should start hissing out the muffler drain hole.
Maybe a faulty/clogged injector in the fuel rail.
JD
