yo NY,
I saw that you have 30 yrs as a Master Tech and that is good to have you here!
Some thoughts from the Tom McCahill days @ Popular Mechanics
Starting with your idea first;
Out-of- Round tire?
Tire balanced?
Are the tires/wheels over-sized, say 33" or larger tires?
Is wheel offset/back space correct?
bad belt in the tire?
Is it Lifted?
Tire - Lift Guide, Bronco & many makes; w/Wheel Diameter, Width & Offset
Source: by Skyjacker®
http://skyjacker.com/images/files/365_tireandwheelcha.pdf
alignment ok?
high water driving?
Wheels and Tires
Inspection and Verification
http://www.diesel-dave.com/vehic/manual/stj/stj44010.htm#extract_753
potholes or uneven road surface? we have the Grand Canyon of all potholes due to being below sea level
is the spindle the same as the other side?
"Spindle Differences 80-96
In addition to the ~'92 loss of a spindle stud (leaving 5) and the addition of 2 notches in the spindle ****** (Bronco only) for the 4WABS sensor used on '93-96 Broncos only, the spindle was also redesigned in ~'95 to match the revised 2-piece inner wheel seal. F150 spindle flanges were never notched or drilled for the 4WABS sensor, but are otherwise identical to the corresponding Bronco's..."
by Steve