Sounds like you should replace the transmission, and if that doesn't work try replacing the engine. And if that doesn't work try replacing the car.
Just kidding! But don't let your mechanics fire the parts cannon at your car! Anything significant enough to repeatedly make your engine stall should be able to be diagnosed.
Maybe a code isn't being flagged but there are plenty of diagnostics a real professional scan tool ($$$$) can utilize. Datalogging, graphs, all sorts of stuff. Find whatever the cause is before randomly firing parts at it.