loss of power

OK I have a 2000 with a 2.2 A/T with 73k, last few weeks it started to loose power,bucking,some stalling NO CODES are being set. After pulling my hair out trying to figure it out i was driving by dealer and car loss ALL power with engine misfire again no codes. In to the dealer it went. He calls me next day and says Cat was clogged and needed replacement. Week later part installed (thankfully under warranty). Picked it up and it ran fine. Next morning symptoms back but worse, now smoking like a chimney and bad sulfur smell. Car wouldn't move Scan tools shows no activity from rear O2 sensor (sulfur smell ??) Still NO CODE car towed back to dealer. He calls today and says muffler clogged b/c of debris from Cat. Parts ordered and will also be covered under warranty.
My thoughts are that something other than exhaust clog is causing problem possibly the ECU (no codes being set/stored) any thoughts,ideas,suggestions, similar experiences with a fix?
thanks.

I had the same exact problem as yours.I have the same year and engine.It was back at the dealers about 5 times. Then somthing wierd happened and a piston rod blew right through the engine block???Explain that.So i just had a new engine put in.The dealer wasn't to trilled, so maybe next time he won't sell ppl crap.

Same problem, the night I bought my 97 Z24 from the dealer, Piston rod blew, he wasnt too happy in the morning with a phone call saying the engine needed replacement. Now I have a free Lubrico warranty because of that, so free engines for 6 months, who cares if I blowem, warranty rules. But tomorrow morning, taking car in so the A/C compressor clutch can get work....maybe it will be covered under warranty.

I'm guessing that "Lubrico" is some type of dealer after market warranty.
Sounds great as long as you can get someone else like another dealer to honor it. I had a dealer after market warranty that was suppose to be $25 deductible "bumper to bumper". The first time i went to use it, the SELLING dealer refused to honor it said they didn't like the companies business practices (WTF). I had to do all the work and lay out the money then wait weeks for reimbursement that was less than the repair cost minus the deductible. Something about the cost of the work was outside customary rate.
Hope it's not a bad engine, if it is the car is history. I only paid $4500 4 years ago for it and a replacement engine won't be worth it.