Dave,

The vibration could very well be your rear drive shaft balancer, located just ahead of the rear u-joiut, or a carrier bearing as you suggest.

To check your steering components for wear, jack up one front wheel and forcefully move the wheel side to side and up/down in order to check the ball joints and tie-rod ends. Secondly, the pitman arm may have some issues. I assume you have a steering stabilizer, most F350's I've seen have one. Disconnect the stabilizer if you have one before the above test.

Pirate has a real good article on Dana 60 axle service. <img src="/forums/images/graemlins/kewl.gif" alt="" />