Mine turned out to be a tire with a slipped belt. No more vibration here!

 

I had the vib for 2 years on my o5 no one could figure it out. I finally solved the problem. traded. I think there is a combo of issues all put together. 1 a cummins is a lot of motor and as in my larger trucks they vibrate. 2 Very rigid frame ( good for heavy work) but transmits vibes better. 3 Pinion angle issues, we improved our truck a bit with 4 degree shim. Good luck

 

My truck also has the vibe going to check slip joint. My vibe is so bad tranfer case is leaking @ rear seal where the joint slips on and at the first bolted split. Got to fix it soon bugging me !!!

 

So far the vibration problem with my truck is not fixed either. I think I'm going to take the truck back to the dealer once again in a couple weeks. This time I am MAKING them physically check some parts instead of driving it, deciding it isn't bad enough to warrent a fix, and then telling me it is NORMAL.