2010 dodge dakota extended cab. Having a mild vibration from drive shaft, or feels like drive shaft. Have replaced all 3 u joints and the center support bearing. Thinking it might be transmission due to feeling a "thunk" every once in a while at speeds of 45.

 

What engine?

 

3.7 liter V6, 2wd

 

Jack up the rear end, (jackstands, please....) and run it. See if anything interesting presents itself. Might also try rotating the tires, and see if anything changes.

 

I was thinking about rotating the tires to see if maybe one was out of balance. I should note that the 3 U joints that I replaced were the unserviceable ones. I read that they were just a pit stronger than the ones with greaseable nipples.