2003 Windstar transmission "rumble"
 

I have a 2003 Windstar with over 200k miles on the original transmission. I know I should consider myself very fortunate to say that.

My issue is that while driving, the engine RPM will suddenly jump 300-400 RPM and the van will feel like I'm going over a rumble strip or vibrate. It lasts only a few seconds and happens imtermittently, only now more frequently.

My description to several mechanics/shops is that they don't know what it is, but will look at it. I'm hoping to learn a bit more before opening the wallet. Has anyone else experienced this?

When was your last transmission filter & fluid replacement performed? You may have a shift solenoid going bad on you. Or it could be clutch slippage starting to occur due to clutch plate glazing (fluid change time). This would cause the change in RPMs. If not done recently, I would have the tranny filter replaced and then have a fluid exchange performed.