After reading back through what I wrote, it does start to sound wheel/tire related. However, I did recently check all the wheels for straightness, put on new tires and had them balanced. The vibration has gotten incrementally worse over time after changing out the wheels and tires (but that is also when I started driving it on paved roads). I may be wrong, but it seems to be final drive related, but I do need to check the wheels/tires/wheel bearings again.
Thanks for the comment.
