I'm far from an expert on this subject; however, here are some thoughts on the problems.
1. If the drive shaft is out of balance, I believe the only way to prove it to be so would to remove it from the truck and have it checked.
2. wheel bearings going bad ususally have some noise associated with them. Either a grinding (if very bad) or some sort of a squeal. In a quiet location, with the wheel jacked off the ground you should be able to rotate the tire/wheel and listen for noise. If its really bad feel the lack of smoothness in the rotation.
3. While driving these noises should show some degree of change as road speed changes.
If your truck is still under warranty, be sure to have the service department inspect it and document the inspection.
I hope some of the true experts can give you more complete and accurate information.
I have no idea but can share a story about something that happened to me once. I had a 1970 model BMW 2002. This car has a rubber bushing thing between the tranny and the drive shaft (bolt bolt to it). I was driving one day and a chunk flew out of the rubber which caused it to become unbalanced. The whole car started vibrating as the driveline spun out of balance.
This of course is a much smaller vehicle with a different setup than the Titan, but I still think that if your driveshaft is out of balance, you would feel the truck vibrate with increasing/decreasing speed as you accelerate/decelerate.
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