What is the Problem???

[68 P.O.S.]

The rear or my truck is lower on the drivers side than on the pass side. What could cause this? Don't say bent frame...

Some background info:
I bought a lowering kit off evilbay (5" spings, nitroactive shocks, shock relocaters, and panhard bar). The guy said it was all 6 months old and he was upgrading to bags so he didn't need it. After installing it all, the whole truck leaned to the drivers side. The PO lowered it by melting the springs...unevenly. So I replaced the front springs & shocks w/ brand new stuff. The rear still leans on the drivers side. I bought a new bed thinking my old rusty bed was the problem... not so. The picture doesn't look too bad, but at my work p-lot it looks like it leans a lot. So I measured from the top of the axl to the top of the frame on both sides and there seems to be about approx 1/2" to 1" difference. But looking at the bed looks way more that that. The front of the truck looks straight as an arrow.

Anyone else have/had this problem? Any ideas, fixes, or what I should check next? How/what do I measure to see if my frame is tweaked?