There is a lot of information on FMCA and irv2 websites about this. Seems mostly for later model Jeeps with electric power steering but apparently there are other vehicles with similar issues. Someone with an Chevrolet Equinox pulled the fuse for the power steering.

In the case of the jeep I saw this "The newer Cherokee 4x4's have electric power steering. Many people reported a severe shaking/wobble while towing over rough roads. Jeep issued a Service Bulletin which calls for a special wiring harness which keeps the PS energized while being towed."

I would call Ford and talk to them about this and they should have have the solution.

In addition to these types of issues, there were several cautions that the tow bard had to be flat. Anything above a 2" difference had the capability to de-weight the front wheels and add to the problem.

Keep us posted on what you find out.