Mcgaughys told me to put in a 4 degree rear pinion shim. This sounds weird since the tailshaft is at -6 now and the 4 degree shim will put the rear pinion at +2. We shall see. Driveshafts shouldn't be out at 4k should it?
Put a 2 or 4 degree shim in, either doesn't matter. Once its in, space the trans accordingly to match the rear. once the driveshaft is at an operating angle, if it still persist pull the shaft and have it balanced.
Normally the shaft will not be out of balance, but as others stated, its still a chance!
Been following this tread so I decided to join. Did a 2/4 drop to my 2014 Chevy 1500 LTZ and had the vibration like QuicksilverZ71. Tail shaft is 6 degrees down and the Drive shaft was 0, the pinion was up 6. Moved the pinion down with a 6 degree shim and all of the vibration went away except when flooring it from stop or when passing someone. Looking at raising the tail shaft next. The -6 degrees is way too much. Shooting for at least -3 on the tail shaft but may not have enough room to raise the tail shaft enough to get there. Not much space between the transmission and the tunnel. Here is a photo of my truck.