The rear diff makes no noise... The other axle was checked for runout and nada. We didnt pull it, but the dial indicator said it was fine (as per the FSM test).

The truck is an automatic, does it has a flex plate? Where would it be if it does?

Where is the harmonic balancer?

The truck still turns the front driveshaft even with manual hubs b/c AFAIK it still has add components in there, just warn manual hubs on the end. Locked or unlocked hubs it

Im waiting to get the bolts/nuts for the rear shaft right now as the originals were hell to remove. Then Im going to pull the front shaft and see how it goes.

Like I said, as soon as you take off the vibe begins and you can watch the x-case shifter wiggle-with the rear shaft on or off. More gas you give the worse the vibe gets-if your easy on the gas you can barely feel it. When it shifts the vibe lessens then the slack gets taken back up in the drivetrain and it goes vibrating again. more rpm, more vibe.

What really left if you think about it?
-Bearings front and 1 rear (the axle shaft I didnt replace)
-Front shaft, the vibe begins in the front and its right under my seat-where the front driveshaft is kinda.
-Or engine/trans? Harmonic balancer someone suggested, what is that, where is it? what does it do?

Im going to remove the front shaft and see what happens, will report back then.