I don't recall if chevys have an offset in the rear like fords do. I think so. Either way I would not use one axle coming up before the other as a diagnostic aid.
You could also be high on the opposite front.
Make sure there is nothing interfering with the shackle's rotation (like an exhaust hanger)
Pull the shocks off all the way around and see if it changes. Shocks should have no effect on ride height.....but, if you have one with a bent shaft it will bind and cause silly shit to happen. I'd pull one at a time so if something changes you know who the culprit was.
That done, you're looking at springs or a twisted unibody.