Leaning to the left, not politically but in my truck.

[jfnar]

My 68 gmc swb sits a little low on the driver's side. When I measure from side to side on the body, it's about 1 inch lower on the left than on the right; front and back. I first thought it would be weak springs but I've crawled around under it with a tape measure and I can't find anything that points to springs. I park it on my level driveway and measure from the ground to different places on the frame and it always comes out about the same from left to right. The body mounts are rough looking and need to be replaced but they measure the same thickness on one side as the other. Is there something else I can check? Do I just need to shim it up a little when I replace the rubber mounts to even it out? I think if it was 1/2" or less it would not be noticeable. Any suggestions will be appreciated.