Well, after driving nearly 7,000 miles like this, it finally got to where I was relatively determined last night to find the problem. I put it in gear, jumped out and walked beside my truck as it drove itself (I don't recommend anyone trying this at home because a +7,000 lb. truck in gear with no one at the wheel isn't the best of combinations. However, my "test site" was a 165 acre bean field, so I had some room to work.) I isolated to to which wheel the vibration was coming from, as I could always hear a shaking of some sort when I hit ANY kind of bump, including driving over walnuts in my driveway. It was from the passenger side, front.
I took it back up to the house and put on my spare to see if the sound was from my center cap. It wasn't because I got the same noise with the spare. I had always been concerned about my remanned caliper I put on when I first got this truck because it moved more than I though it should.
It turns out that I neglected to put the rubber o-rings in the grooves inside the casting where the steel sleeve goes. I had them sitting on the workbench the whole time, though and just kept walking past them. I fished them down into their respective grooves and BINGO - no more rattle and no more clunk. Wish I would have thunk this up a few miles ago!
Thanks to all that offered advise on this, but I didn't mention that I had replaced the caliper because I had forgotten. My mistake.
Snowman