Ford SuperDuty more bumpy + jittery empty, than when loaded?

My family has had Ford's for years. We've had good luck with them but I've always thought they were a bit worse on washboard type of roads than the others when empty. The old twin I-beam were a real handful on washboards, at least now it's mostly just the back end moving around. I've driven gravel roads most of my life so I'm mostly used to it now.