I occasionally had a similar issue on several mid 90's superduty series truck. Turned out to be the bushings in the dogbone on the front axle. It would only do it on 2WD trucks. I don't know the technical name of the "dog bone", but, this piece will be obvious. It goes cross wise in the suspension, and basically looks like a long dog bone. The bushings were pretty cheap, and you just unbolt it, put it in the bushings, and bolt it back in. It doesn't require a front end alignment afterwards. As far as the newer trucks, I don't know if this would be the same issue, but, if you have the dog bone, replacing the bushings may help. And, it will be real obvious by looking at, and wriggling the part, if the bushings are bad.