Overdrive light comes on and continues to blink in my LX 626 1995

I have had the mass airfow sensor replaced, caused problems until my mechanic figured our broke things in transmission as it would all of a sudden run/shift poorly. After he had replaced computer/ rebuilt the transmission etc and tuned it up it ran great. The OD light came on and, it didn't lose overdrive but it sure shifts funny when its on. He came to drive it and have it hooked up to a computer but when he turned it on the light stayed out and the computer doesn't store info. So it sat for a while and when I went to drive it it was great but 80 miles into me driving it the light once again comes on and at times if you step on it it will shift really hard. It still has overdrive but I don't want to break anything again. My mechanic transmission specialist is scratching his head. He has told me so many things influence the running of the transmission in this car. I am 2 a total of $3000 in repairs and at this point I can't sell or trade it so I would like to figure out so I can drive another 50000+ to get my money ot of the car. Thanks Zane