When my F53 was brand new I had a problem with keeping it going in a straight line. I would make a steering correction to one side and then have to make another correction to the opposite side. Making constant corrections wears the driver out pretty fast.
The RV dealer had me take the unit to a wheel alignment specialist who found that the right king-pin was occaisionally seizing up hence the need for constant corrections. Ford, because the unit was under warranty, had me take the king pin assembly to a machine shop where they reamed out the bore so it was now free to move all the time as required.