I am having the same/similar problem with my 2000 windstar SEL. I first noticed that it would not hold the overdrive while on the highway with anything more than barely touching the gas pedal. After a long drive it would only shift into overdrive if I was not touching the gas. During the completion of a long trip, my O/D light would blink but reset the next time I started the van. The transmission would behave more normally when the engine was cold but once I had been driving for a while, the overdrive issue returned. I had the transmission flushed and replaced but no change. Anyone have any idea?