I'm kinda with Fred.... Considering the symptoms started after a bump in the road, a problem internal to the distributor could cause this. You symptoms fit a distributor that has gone retarded. I mean that in the literal definition of the word. It sounds like spark is no longer advancing.
I am assuming they have plugged in live shop computer to verify the signals from each of the necessary sensors? Has a cylinder balance test been done? Has the A/F ratio be verified?
At this point, it sounds like the shop is just throwing parts at it, and some of the parts changed should not affect drivability like you describe.
