My 1993 Aerostar has trouble going into overdrive.

i have a 93 aerostar 3.0l overdrive. it has 225k plus miles on it. the engine is original and i believe the trans is too. problem: going down flat road with cruise on or off at 55-60 mph. check engine light is on and transmission is not going into overdrive. then it will shift into overdrive and the light goes out. it may go for a fwe seconds or minutes like this then the light comes back on and a few seconds later it comes out of overdrive. i have had this happen several times during one 4 mile trip. any ideas what to do with it?

Welcome to this forum! I've renamed your thread, and moved it into the Aerostar section. You have to scan the computer to see what the code numbers are for the check engine light.