Check to see if your steering box is TRW or Sheppard. The TRW box is the better of the two. Time to check the front end, tie rod ends, drag link, bushings, etc for looseness/wear. There is an exhaustive discussion on another forum titled "wandering, sway bars, oh my!" Search 'Monaco Watts' for a possible solution.
I have the TRW box and have adjusted the play a bit, much better now. But I will say that I know it is very easy for me to 'overcorrect' the steering when I drive; I now pay attention to my steering corrections!