Meaning that each is lined up with the other, instead of being clocked a little wrong.... but you have had 3 different d-shafts in it so I would say that you have eliminated that(still just guessing)
How bad of a viration is it at 80mph and what does that translate to in rpm at the engine... its a rpm issue and not a speed thing. I'm sure that if you changed gears in the rear that the speed of the vibration would change so its all about rpm of any given component
at 35 mph there not to bad but 80 ther real bad, i think the rpms are around 5200 at 80, this is with 4.30s
