Need help diagnosing vibration

Hello all. I have to first say that all u-joints are tight and I just had the center support bearing replaced, as it was completely trashed when I bought the truck.

The vibration only occurs during load at highway speeds (over 60 mph). So if I am slightly accelerating, I will get a noticeable vibration (I believe I feel it in my feel). But as soon as I let off the gas, it goes away for about 3 seconds, until the truck starts to really decelerate, which it comes back slightly. So in "suspended" speed, where it is NEARLY constant, there is no vibration.

Does anyone have any ideas about this?

 

Does anyone know if something like this could possibly fix it?

http://stores.streetacos.com/-strse-1/carrier-bearing-driveshaft-vibration/Detail.bok

 

bump....

 

Any other suggestions?

 

So I am the only one that this has ever happened to lol