"TLR—Tire/Wheel Lateral runout: Vehicle speed
sensitive, mechanical vibration. The runout will not
cause vibration below 50 - 55 mph (80 - 88 km/h). Excessive
lateral runout will also cause front-end
shimmy."

This sounds like my problem. Manifested in my case as steering wheel shimmy at 55-65 mph. This only occurs when one particular wheel (tire & rim) is on the front end.

Your testing technique sounds promising, but I don't own a floor jack or jackstands. And the auto skills center at Nellis AFB is inaccessible to me (due to the base's Covid-related access restrictions). If I could get out there, I could put the vehicle on a lift.

I think tomorrow morning I'll look for a tire or other shop that will check it for me (while I watch like a hawk). Interesting that DT never suggested doing such a thing. Even though it might give them the chance to sell me a new rim.