While I'm at it, would low fluid In a transfer case or even a cracked housing cause a really fine vibration at 70-75MPh? I also noticed when I decelerated it made a really low pitched hum. I'm fearing a tranny failure might be in play here too. If my tranny is almost done I won't have a vehicle anymore.

 

Trans won't really give you a vibration without some other truly interesting noises/symptoms as well. More likely you have a tire slightly out of balance. Rotate your tires, see if the vibration changes/moves.

Low fluid wouldn't cause a vibration immediately, but, the snap ring being gone sure could.

 

Hi all. Registered just to give some info to those that might have wandered onto this post searching symptoms like I did. I don't know if it applies to other models, and know the OP doesn't have a same year truck as me, but the same thing happened to me today. Ends up there was a recall enacted Dec 2014 for the 2005 1500 (recall P77) where the drive shaft disengages from the pumpkin. It did on mine tonight and ripped my transfer case in two.

Very scary stuff.