On my late model truck I run a 295 tire and when I get on the black topped roads that the semi's travel it gets really hairy. My truck is a late model suspension 2001 with really low miles and so I think you hit it correctly with the wide tire you are using, it is railroad tracking in the grooves-coupled with the ancient steering and suspension = scary ride. I'd be willing to bet you get a narrow tire/wheel radial on there, it will be much better, but it will still be there, not a lot you can do about it IMHO.
1953 Chevrolet 3100261 cu inch, sm420, 3.55 rear, torque tube still,omaha orange, still 6 volt, RPO green glass, side carrier spare, all done
In the DITY GalleryVideo of the 261 running1964 GMC 1000305 Big Block V6, sm420, the next cab off restoration
