Vibration

[47jailbar]

I doubt it’s wheel/tire related as there is no vibration at low speeds and seems to be more dependent on engine RPM; at shift points and above 45 mph in third. No tach installed at this time however by my calculations 275 60 15 tires with a 4:11 gear would produce a driveshaft rotation in the neighborhood of 2220 rpm at 45 mph which would also correspond to a reasonable shift point.