i get vibrations like that too (as the original post mentioned). Mine only get noticable at 70 or so mph but get worse all the way up till like 90+ mph at which point i think there'* enough wind noise that i forget about it
Anyways i feel my vibrations a little longer and throughout the mph range. Example I can 'feel' some sort of slooow vibration at 20 mph sometimes. Feels less noticable than at 75 mph but i feel it still there and at a much slower period of oscillation if you will.
I've replaced inner/outer tie rod ends because that used to cause MAJOR vibrations at 40mph+ and it definitely fixed that. THis vibration must be ball joint or something else because its not the tie rod end vibration. That one felt more like the wheels themselves were vibrating, this feels like a chassis vibration.
Let me know if you replace the ball joints and it fixes somethins