I'll see if I can link the video when I get home, I don't have it here, but unfortunately you can't see anything. My friend was actually confused at first because he thought nothing happened, and from outside it looks fine, all this time I just assumed it was wheel hop because from my perspective I just felt shaking.

yes I have checked all of those things and they are all good.
I have a needle bearing pilot in there and it was new just 6000 miles ago.
The weird part is that it runs perfectly smooth at any rpm, just as long as I'm not spinning the tires. It starts shaking immediately as soon as I have the clutch out if I'm on it hard enough to break the tires loose, I can get on it as hard as I want with no problems as long as I don't break those tires loose.
The trans is what starts to shake back and forth, and since it's a truck I have a big long stick coming all the way up from the floor and it starts bouncing back and forth sideways so violently I always get right off it.

I do have a 3600, so it is a full bed, and my driveshaft is over 70" long. Are there any rules of thumb for max driveshaft length? I know I've been looking at our full size trucks here at work, and both of them have intermediate bearing supports and two piece shafts instead of one long shaft.
My driveshaft angle is very mild, so it's not like I have crazy U joint angles or something, the truck is very low so it's just a few degrees on each end.