2001 Ford F350 Shaking

#1

I have a 2001 Ford F-350 4 X 4 with 43000 miles, automatic transmission.

Tire pressure is as recommended 55 PSI on the front and 70 PSI on the rear since I’m not hauling anything heavy.

My problem is that I have a bad vibration or shake, it starts around 20 miles per hour is the worst between 30 and 40 then starts to smooth off again. It is also worst under acceleration.

I rotated the tires at around 35,000. I know I wanted to sooner but those rears don’t come off very easy. Since rotating I have had this vibration. I thought it was maybe because the rears had worn with a flatter surface and the lugs on the outside of the tire face where making the vibration, since the fronts wear with more of a rounded edge. I have had the tires spin balanced still doesn’t help.

Did I get a poor balancing job?

Will it smooth out after another 10,000 miles and my teeth fall out when the side lugs round out?

Or could something else be out of balance?