Odd problem- rearend not centered?

[TugOwar]

dana60 rear end with leaf springs

When I put the 700r4 transmission in my GMC I went with a one piece drive shaft fabbed up by Drive Shafts Unlimited in San Antonio. It works great.

However, something (rear end?) is off center. The drive shaft doesn't pierce the center of the hole through the cross member, it sits closer to one side. This only becomes a problem when I add a bit of cargo. A few hundred pounds is enough to make the drive shaft rub against the SIDE of the cross member, not at the top as if the springs/shocks were bottomed out.

Stand at the front of the truck and look down the sides of the truck you can see the passenger side rear tire sticks out from under the fender slightly more than the drivers side tire.

I'm not sure where there is any place to make adjustments. If the saddles are welded to the axle housing (are they?) it's not like the rear end can slide to one side. The U-bolts are tight, I've checked. Where to go from here?