vibration around 40 mph, tires have been changed and aligned. driveshaft lost balance???????????? i have no idea but this has done this for 3 years and i just really want to know what the heck it is. driveshaft would be a whole lot cheaper. it never gotten worse or better. thanks

 

Have you tried changing the oil in your Torque Converter.

 

If yours is four wheel drive then you might check the front driveshaft also. Even when it is intwo wheel drivemode the front driveshaft will still turn and cause a vibration. I have had 3 different Expeditions that needed front driveshaft u-joints for your same complaint. Just a suggestion.