NEED HELP! Bad Vibes in 4WD

Got my truck back today after he gave up on trying to figure out the problem. Went to Yodaman and he suggested i do a diff drop to start. I've heard those are no good, so not sure that's the route i want to go.
For now im gonna put new bearings in my spare shaft extension and swap it with the one thats in the truck.
If that doesn't fix it, I'll let ya know about pulling the whole thing. Extra hands definitely will be appreciated

 

Well I finally got it figured out and the truck put back together.
Turned out to be the crush washer in the front diff was installed incorrectly and was seated crooked. That caused everything else to be crooked and in turn caused a bad vibe. Go figure. I sent the front and rear diff to ECGS and they went through and replaced everything that was messed up because of bad install(not by me). They said they never use a crush washer and replace with a solid spacer from the start. Cant say enough good things about them, highly recommend. Lesson learned, just buy new

Truck runs great. Smoother than ever. Since it was immobile for a couple weeks, I was able to get some other things done. With the help of some good buddies we also installed a snorkel and fitted for 35s along with some other stuff. Can't thank them enough!!