Mitsubishi Repair: Automatic Transmission shifting problems, mitsubishi lancer glxi, magnetic sensors

Question
Good day Ms. Linda! My name is Von and I am from Manila, Philippines. I have a 1994 Mitsubishi Lancer GLXi with 4G92A engine and automatic transmission. The problem is that there are different shiting problems occuring in different times. More often, the car just sticks to 3rd gear and from what I've learned, 3rd gear is the default whenever there's something wrong with the transmission's wiring/computer or sensors. Is this correct? So if it is, then maybe it's coming from electrical parts, not mechanical I guess. For me to temporarily resolve the problem, I am switching off the engine and then starting it again and there it is, comes back the complete gearing. And after a matter of time it will be on 3rd gear again. I have already changed the fluids and cleaned the strainer, but still it occurs. I also tried to change the sensors (the two magnetic sensors clipped to the transmission), it worked but after 2 days it comes back again. What could be causing this? Most mechanics in my country are suggesting to purchase a rebuilt or surplus auto transmission but I still believe that it's just on some minor parts especially electrical. Another problem is that sometimes the shifting is delayed and sometimes it is advanced (but the gearing is complete). And when it happens, it is usally followed by the first problem afterwards (the 3rd gear sticking). The car has been like this for 8 months now, and I really don't know what to do or replace. Is there another speed sensor that I can try to replace (because here in my country we can easily acquire surplus/used/bargain parts from Japan) and I am willing to risk trial and error instead of purchasing a rebuilt/surplus transmission which will cost around $220. Can you help me? Thanks a lot and best regards

Answer
Von: Have you coded the computer? The computer controls everything in that car of your's. If you shut off the car, then restart it and things work good for a while, then computer is resetting its self. But soon back to the problem, it is all caused from the computer. It is picking up a problem in the system, but your car is the right year for the bad computers so it might be the computer its self. You can either have the computer rebuilt or buy a new computer for your car. I would try that before replacing the transmission because if the computer is bad, once you put the different transmission in the car with time the computer would mess with that one too. Take care... God bless: Linda