I just noticed that the ***-end of my truck is 1.5-2" lower than the right. It doesn't look like the front is, just the left. Now, I'm pretty fat, but I don't think the 8000 miles I've put on the truck would be enough for my fatness to cause the spring to sag.

Any ideas of what to check short of replacing the spring? I'm not leaf-spring savvy at this point, as this is the first RWD vehicle I've owned (all others have had struts in back).

 

I just went outside with a tape measure, and the left side measures roughly 19" to the ground from the little bolt right behind the tire on the bottom of the body panel, and roughly 20 on the right-- while the left rear spring mount is about 1/2" or less lower than the mount on the right. I suppose that means the box is bent. Awesome.

 

Not necessarily. When mine was about 1.5" lower on the driver's side, it was because of a weak driver's side leaf spring. The measurements where the leaf springs rested on the blocks on the axle were almost identical, but to the body it was off (sounds very similar to your situation).

I replaced just the driver's side leaf spring, and my driver's side is now 1/4" (approx) higher than the passenger side when I'm not in it.