I do have a bad downstream 02 sensor.. but it didnt act like this before I changed my stock muffler and put a super 40 on it... I checked all the sensor's, tps, map, cps. all of em. their all in working condition.. no vaccume leaks nothing.. And no when it stumbles and if i go WOT it will jus die hard!!! I hafta let go of the gas,, and gradually and i mean gradually get into the throttle.. Im thinking a weak battery or a bad ground could be causing som kinda of mis- fire. bc at times.. it doesnt have any problems..like yesterday it ran fine for over an hr with no problems.!! But today.. with it raining.. ugh the worste Ive seen yet.. Plus While it was acting up inmy driveway the Volt meter was at 14v, and when it was acting up it was falling to almost 0v..to like 2 or 4v. but when its not stumbling or stuttering shes back at 14v.. So when it stops raing Im going to check grounds and connections.. maybe take my battery to one of the parts store to take a Load Test