You could pull the front driveshaft out and put it in 4WD and drive it. That should lock the front end in. If you still have a vibration, it would likely be in the front axle. If not, the transfer case. If the vibration goes away, it’s in the front driveshaft.
Since its sitting on jack stands, I think I'll try going 4wd low and back. I am thinking transfer case/transmission. I will pull the rear diff cover off just to check, but it was all rebuilt in the spring. Anything is possible...
