I had this happen in my 5000 when I first got it. Scared me pretty good being in a big truck with no power steering with death wobble.
My remedy (as SweetK30 has said), get a steering dampener. I installed one of the draglink and so far so good. If you hit a man-hole cover the right way it wavers just a bit, but a quick jerk on the steering wheel keeps it from going further... new front shocks should take care of that (still has originals).
I have an IFS front end that is a bit worn and old bias plys.
Steering stabilizer is for a motor home, was the heaviest one I could find on ebay. A Roadmaster Reflex.
