2003 F53 runs smoother above 70 MPH

Is your vibration felt in the steering wheel or in the seats? If in the seats I would look at the tires. When I had this problem the seats would vibrate but the steering wheel was fine. I jacked up the front tires off the ground and put a flat piece of wood under each tire then spun the tire by hand and measured the run out with a crude feeler gauge I made. My tires were 1/8-1/4 in out of round. I marked the high spot with chalk and let the MH sit on that spot over the winter thinking I could reshape the tires enough to smooth out the ride it helped slightly. Rotated the tires to the rear thinking maybe they would wear better in the back, still a vibration in the floor/seats. Lowering the tire pressure helped some, tried to find a place that shaves tires, nobody in my area does that anymore. Finally bought new tires and the problem went away. No amount of tire balancing(tried Equal also) will fix an out of round tire.