It turned out to be the driveshaft. One of the drive shaft to differential nuts and bolts fell out. It's back to normal now after replacing it.

Wow, I guess balanced means balanced, right? I know the driveshaft is balanced and weighted, guess if the diff is no longer balanced the whole thing vibrates.
Glad you got it sorted out, we've all learned something.

yeah, Im going through the same problem right now. However, all the nuts and bolts are secured down, so I'm not sure. Once I conclude what the problem is, Ill make sure to keep you all posted as well.

Thanks modme.