High speed vibration and grinding noise

['63GENIII]

When I swapped in my 4500, It took a while to get the rear end shimmed correctly. Then a year later, while swapping the rear D60 for a 14BFF, I was at it again only this time I was able to set the pinion angle and weld the perches in. At that point, even though the 14 bolt pinion was shorter than the 60 by 1 or 2 inches, I still had to put a 1/8" flat shim under the rear of the transfer case mount to get it back in place. It took a bit of time to get it right and the adjustment was very minor but made a huge difference.

I suspect that you'll have to get the DL angles right before attacking the transmission sound. I could see the vibration wiping out a bearing or bushing in the trans pretty easily.