Vibration at 3200 rpm and above need help

supershafts
If that was addressed to me; I had one shaft balanced for the 4.3s, and told the shop I wanted it as smooth as possible at 60mph and hopefully up to100mph.They didnt get it right the first time, so I had them do it again.The second time was better, but not by much.It was quite smooth on the jackstands.
I used a different driveshaft for the lessor chunks as the yokes were different.
I tried several different pinion angles.
It only did this at 55 to 60, and only with the 4.xx gears, and only really noticeable when cruising. I therefore attributed it to the natural body rhythm, somehow being excited by the D/S speed with the 4.xxs.

I soon pulled the 4.3s, cuz around town 1st gear was useless most of the time. I swapped in 3.55s and a 3.09 low gearset. problem solved.

I recently sold the 4.30s to a fellow with a Coronet. He hasn't called with a complaint yet.