i know it's a band-aid........ BUT
do you have a good steering stabilizer on there?
i went through everything on my rig including taking it to a place that measured the frame and verified it was good and nothing fixed it for me. I am talking every component was touched and replaced. axle housing is the only thing I didn't touch, but the frame shop said it was good.
A new steering stabilizer fixed it. band aid i know, but i was ready to sell the truck. My old one had a dead spot in it where it ran 99% of the time.