I'm joining the club.
2005 Sport
Dana 30 Front (new hubs and u-joints), Dana 44 Rear (new bearings)
4.56 Gears
E-Lockers
Adams Driveshafts front and rear, both have been properly balanced
Savvy control arms, so the pinion angles are dead on (but the control arm bushings are poly)
NP231 transfer case with Advance Adapters SYE (rebuilt and runout on shafts checked)
42RLE transmission
Motor mount lift with new Crown motor mounts
Stock transfer case skid with a new transmission cushion
Sitting on 33s now, but the vibrations started while I was still on 31s.
Like
@bobthetj03, my vibrations are only related to the speed of the driveshafts and everything directly connected to them. Engine RPMs and transmission shifts don't have any effect on the vibrations at all. Also like others here, my vibrations go away if I pull out the front driveshaft.
While I was diagnosing the problem, I got some vibration data from the Spectroid app on my Android phone. Here's what it looks like.
The peak at 64 Hz is ordinary engine noise. The peak at 32 Hz is the driveline vibration hum. It actually starts at a slightly lower frequency as I accelerate into the range where the vibrations pick up, then moves up to 32 Hz as the vibrations get worse. If I accelerate more, the amplitude increases but the frequency stays at 32 Hz.
Also, for what it's worth, I tried swapping in a Prothane transmission cushion, thinking that the polyurethane might make a difference. It did. Instead of a warm, sine wave hum I got a harsh, louder square wave vibration. That was not an improvement, so I switched back to the rubber cushion.