My 1989 dodge b250 318tbi with push button overdrive transmission has been dropping out of overdrive and then back into overdrive. I changed the filter and trans fluid with ATF+4 and installed a heavy duty trans cooler about a month and a half ago. I also put in lucas trans conditioner with the change. it only started to have problems after the fluid change. The vehicle has 18300 on it right now. I have put 50,000 on it since I bought it 2 years ago. I changed all fluids after I bought it and didn't have any trans problems after the first fluid change. Anyone have any idea as to what can be going on with it. Thanks for your reply.19898

 

My first though would be the OD solenoid inside the tranny is weak and unable to hold the OD engaged.