My car has been stalling and shutting down for the last four months, what should I do?

modern vehicles are mostly computer controlled after getting inputs from various sensors, so a good mechanic with a scanner should be able to read the data going into the computers to see what is going on and then to work out a diagnosis. Seems to me you dealer is not doing their job. I would recommend taking to another shop, one that is AAA rated with ASE certified mechanics. and ask if they will guarantee their work. Or you could ask your dealer to fix at no additional cost since they have failed to repair after 3 times. If they say no; report to your states bureau of automotive repair.