Good thread... I wonder if I am having the same problem. Suspension / motor mount.
For back ground I have ~25,000 miles on mine and is a great in all aspects (imo) , nearly 40 on highway trips, except one very bad and potentially big problem. Serious vibration at 55mpg (also at other speeds but 55 is the worst), from the transmission according to the dealer. "First order vibration" Really?? I was told "that is the way it is, new ones do it too".
Funny, mine didn’t start till after 20,000+ miles. I drive the same road everyday, twice a day for the past year and the road has not changed but the car has. When I drove a brand new one recently, no vibration. I can get past the transmission feels different, you feel shifts and some vibration when you are stopped in drive. BUT driving at normal speed it is enough to vibrate a bobble head on the dash. Initially it was thought to be a tire problem.
One tire on the car was worn out at 25,000 miles, down to the wear bars and out of round, you could physically see different sides (of the tire) of the road contact patch was not worn evenly. Continental ContiProContact 215/50/17. I think the tire change treated a symptom but not the real problem. Probably something wore that tire out, it certainly wasn't not that lack of wheel spinning power. It sort has that convertible cowl shake when it hits a bump, sort of settles out verses soaking it up.
After a set of 900$ Michelins it still vibrates, maybe not as bad but obviously still there. I am willing to bet no one in the world want to invest 20 some thousand into a car that vibrates at 55 mph after ~20k miles. I will let you drive my car... Ford has been far less than helpful. Hopefully a FSE will look at it.
Wit all that said, I am pretty unhappy at the moment.