transmisson slips when going from 2 to3. Over drive light flashes all the time. on 1997 Ford Explorer

The OD light flashes wheather it is on or off. now the transmission slips betwee 2 &3, or pulling a hill. No slipping when pull off. fluid level is full.
Does the ECM control this also?

Asked by for the 1997 Ford Explorer
take it to a tranny shop for diagnosis