2003 Ford F-250 violent oscillation

I have spoken with several F250 owners around my year model and they all say that they have had problems with a violent shaking and oscillation of the front wheels and steering wheel. My truck has this problem between 30 and 50 mph and usually happens after hitting a bump or a rough spot in the pavement. Sometimes I can turn the wheel back and forth and which will cease the problem, or I may have to speed up or slow down outside the listed speeds. All of which are dangerous depending on the condition. I have looked at the bolt connecting the pitman arm to the column and that is tight.