2016 3.5l ecoboost, 145000 miles. To my knowledge the transmission oil have never been changed. Im getting a vibration, no clank or rattle just subtle vibration thru the truck, (its not the tires, wheels or alignments; thats all been ruled out) not the steering wheel. It happens for a 1-3 seconds then goes away, then comes and goes through the drive but at no set times, random. Few things i noticed is......only happens while truck is under acceleration and or cruise control, so it wont happen when the gas pedal is not pressed or in neutral, I did put it in 4wd and it did it in 4wd also. Happens at 40mph and anywhere up from there.

 

Sounds like your getting "Torque converter shudder". Wish I could find the link(s) on the web to help you.
If you google it, you should be able to find similar complaints.

 

I had that happen around 106,000. Drop the pan and replace with a new pan with a drain plug. Replace the filter and what ever fluid that drains out. Add one tube of lubgaurd shudder fix and top off with new fluid. Then do the same thing at 30,000 more miles then again every 60,000. Took me months to figure what was wrong while the dealer always said nothing was wrong while under warranty. Go figure.