It feels like it is coming from the rear end area.
When I accelerate I can feel the vibration, when I let off it is NOT as present, but still there a little,

the faster I go the more vibration there is.

I'm thinking
1. U-joints
2. Rear End

However, I'm simply guessing (THOUGHTS?)

 

U-joints, maybe, rear end doubtful. The rear end is a pretty solid asembly and everything that rotates is contained by bearings. A vibration is usually something out of balance and unless the companion flange (input yoke) on the rear end is loose, there's not much that can vibrate without failing completely. The driveshaft does see greate torsional loading on acclereation, but at high rpm, the rotational forces themselves are usually sufficient to cause the vibration to occur on both steady state and acceleration. Where does the vibration come in and where is it the worst? Does it go away as a function of speed or only load?

 

IT is noticable t higher speeds, however much more present during aceleration as compared to deceleration.

the faster I go the worse it becomes

 

I've been through chasing a vibration on the SS lately. 4 u-joints later, It boiled down to a combination of a worn out trany tailshaft bushing (special puller needed).
And the DS was not centered. (used a dial indicator and differing sized c clips to get it centered)

If your vibration differs with load... Try looking into motor mounts and the rear tranny mount first.

Rich