Yet Another Update
OK, I went to the balance shop in South Atlanta (Atlanta Powertrain, great guys, ask for Mike Romines if you go there, and tell him Daniel sent ya), he made sure that the u-joints that I installed were done properly, which they werent perfectly installed, so he re-did one of them, and made sure it was all good.
He then put the shaft on the balancer and spun it about 2,000RPM, he immediately noticed a visible inbalance, so he did this cool thing where the spun it up fast, barely touched a peice of chalk on either side of the shaft while it was spinning to mark the high-points, and then he took a torch to the chalk line and then immediately ran water over it, about 3-4 times each side, after he did this, he spun it again and it was perfect (this guy knows his stuff), he didn't even have to put weights on it.
SO I got home, installed the shaft, and took it for a quick spin. Unfortunately, it didn't solve the problem, however it did make my accelleration smoother and also seemed to lessen the vibration about 10% or so.
I then decided to move my tires around, because it is cheap (free) and a quick way to determine if my tires really might be the problem. And guess what? I've had my tires balanced 2 times, and each time nothing helped, BUT this time, when I rotated my tires, the vibration almost went away, it's still there, but now it's in the front of the truck, and it's much more subdued, so now I know that I need a new tire (I'll probably spring for a set later on) and I've almost totally rebuilt my suspension chasing this thing down. I think kontan said he thought it was a wheel/alignment issue, and he was right. I'm going to go back to the tire shop and see if they can road-force match the tire to the rim, that may eliminate it as well.
I'll let you all know what happens. Guess I can take back my mounts and get some money back to put towards tires!
To anyone going thru this issue, try rotating your tires one side at a time, or both at once and see if it makes a difference, then you will know it's something to do with the tires/wheels.