5x5 ss wheels shift on 1971 rotors

[luvbowties]

We put a set of 1988-1992 Chevy pickup SS wheels on 1971 rotors using the 1/2" fine thread studs and lugnuts--the lugnuts with both internal and external threads(external to hold on the center caps). Hit a light to medium pothole, and the victim wheel will be knocked 'off-center' and "cam along" instead of rolling true. Always on a front wheel--never a rear.

Can remove & replace carefully, torque them to 80 ft-lbs, run true until another pothole, and it will do it again.

Any ideas to correct this problem?
Thanks,
luvbowties