I bought a 2019 f-150 new. I had a vibration I would feel on my seat at 41 and 70 mph. Over 3 years Ford could not find the problem. I changed the tires from stock to lt tire, the vibration at 70 stopped. Ford changed the drive shaft, no change. Last year I was on this forum and someone posted that they changed the transmission fluid so I did. So after 5 years of Ford saying it was within tolerance the problem went away. Thank you