Car is hestating every once and a while, jerking you in the

I havea 1998 Honda Accord LX, 4door with 96,500 miles on it. Recently the transmission was rebuilt and the cat converter repaired. The car has been brought back 4 times for the transmission and the last time the shop kept my car for two weeks and replaced valve covers and gaskets. However, one day after getting back the check engine light came on. My mechanic said it could be an o2 sensor, but the hestation when accelerating is starting up again, I am getting so fustrated with this, because we have also had the ignition switch chamged. Any ideas as to what the problem could be, I don't think there is anything wrong with the tranny anymore, but what is causing this delay in acceleration.