Overdrive light flashing on/off

Ford 350 turbo diesel 7.3 1997 dually pick up. Overdrive indicator light flashing on/off. I purchased the the truck with a bad transmission so I got it rebuilt then I put 22.5" semi tractor trailer wheels and tires did a lift on it and put a bigger transmission oil pan also a temperature gauge for the tranny what can be the problem it seems to work fine one day then the next it wont work at all when the light turns on it shift very hard then when the light is off it shifts fine ohh and I also put a shift kit on the tranny please help invested alot off money and no one seems to know the problem thankyou mike