I thought if your check your caster and itś ok, your other point itś your U-yoints in the rear drive shaft. When i had my HJ-60 SUA I had an strong vibration BTW 60 - 80 km/h.
with the SO conversion, I assure the the pinion get proper angle to work, and right now with SO and 10" of lift, I have no vibration on highway ..
with the SO conversion, I assure the the pinion get proper angle to work, and right now with SO and 10" of lift, I have no vibration on highway ..