Dual wheel vibration/ shaking

[RoyBoy]

Have had a vibration problem on truck in sig, here is what I know for sure. Tires are all balanced perfectly. (I am using Ride-on balancing/sealing compound) If I run either the outer or inner rear wheels, vibration is gone and truck rides perfect right to 100.
I just had my wheel spacers at the machine shop, and I personally replaced the center rings and made them thicker and longer (to catch all of the outer aluminum wheel). I might have a little less vibration now, but it's still there, and it's driving me crazy!

 

[powerboatr]

did you have the run out checked??? the wheels are hub centric, is it possible your spacers are off slightly and not sitting true on the hub???
ours vibrated at 100 as well but it was on a dyno at the time