My vibration returned after 300 miles. It has been at the dealer all week and the Ford engineer has said that the vibration is still within spec. So looks like after a new driveshaft and the hose clamp balance, they have given up.
My 2016 MT-82 GT had the same issue around 70-75 ish. I took it in and they replaced the driveshaft, but it still vibrated. So they used the vibration analyzer and found the new one to be out of balance. They balanced it with hose clamps and it reduced the vibration to almost nothing. Its still...