That is exactly the symptoms I had.
1. Hard shake on take-off, especially when towing or hard acceleration.
2. Vibration which starts around 70, and worsens as speed increases.
Note that #1 can be caused in leaf spring vehicles that have no sort of anti-wrap control on the drive axle, but it would be really hard to wrap the springs on an F550, and I do not think axle wrap is the issue.
That said, I do have a little shake left on take off when towing and hard acceleration, but the vibration over 70 is completely gone after Ford made the repairs.
