5/7 drop drive shaft U-joint ???

[bark]

Hello, I have a home grown 5/7 drop on my stepper, and was wondering if any one has had drive line vibration, or what you are doing to set up pinion angles, I did a bunch of research on the good ol net, got confused, and found that you are supposed to match the angles from the trans to the pinion, but I think it will be better to try to run the diff straight with the shaft.

rite now my trans tail shaft is headin down hill and my pinion is facing up hill, (which is matching like the net says) but I have a vibration (shimmy) in the floor boards, or seat that starts at about 40mph and quits at 50, on acceleration, and deceleration. I've had my tires balanced, the shaft has no dents looks straight, new joints,new shocks and got an allignment. Its driving me nuts, do I need to shim the diff and or raise the tail shaft? Might have to pull the shaft and get it balanced as well

What have others done, or is it maybe something I'm over looking?