I am still curious. Has the OP ever driven his dad's truck and fifth wheel?
It is very possible there is no problem and his dad has gotten to the stage where he may not be able to tow a large trailer.
We all have to admit anytime a large truck goes by at 10-20 mph faster than you are there is going to be some push regardless of the tow vehicle you have especially if there is any significant wind.
As for me I do not really notice it but when I look back and see this large trailer that is much larger and heavier than my truck I often think if in an emergency maneuver the result could be real bad. If you think about that too much then large trucks may cause you problems.
His father just may not be able to handle that now.
