Transmission problem with fan on.

What is your question?

I have a 1999 Mitsubishi Eclipse Spyder GS with an automatic transmission. The car drives fine and has been well taken car of. Recently it has developed a problem with the transmission while the cabin fan is on. Like I said the car drives fine, however when I turn the cabin fan on (the one for AC/Heater) the transmission will downshift, then upshift, then downshift, etc. It will hunt for the correct gear for about 15 seconds or so (as seen by the RPM speed), it will eventually settle down, but as it is I can not use the fan while driving as I don't like what it is doing and I'm afraid it will cause further problems. I can use the fan at idle no problem. This problem happened suddenly with no warning. I have checked everything I can think of. Battery, alternator, wire connectors on transmission, grounds, relays, fuses. I don't know what else to do. I have also searched Google for others with the same problem but didn't find anything. Any help is appreciated.