1996 Subaru Legacy engine miss-fire

I have this problem for the past 2 years. The engine of my 1996 Subaru Legacy always miss-fire and stalls at the same geographical places. By coincidence it happens to be always in front of a hospital or an medical office that provides X rays images. I have sent it to the shop many times. The scanner codes always reflect Miss-fire cylinder 1, 2 3 or 4 (it does not manner it is always a different one). I have already replaced the Cam and crankshaft sensors, computer module, the sparkplugs and wires, ignition coils and nothing is fixing the problem. I can drive many hours during the day without a problem but at soon as I get nearby to the medical office close home, the cars stalls, right there. I am suspecting some sort of problems with EMI (electro magnetic interference). What can I do to fix the problem? I will appreciate any help you can provide me in regards to this issue