[Coupeguy2001]

If the axle is flipped, you will probably end up adding longer shackles to the high side for a cheap fix..... however,
Usually, if the frame is straight, there is a problem with the spring.
If the spring has a problem, you might try getting a matched pair, or taking the truck to a spring shop, and they can re-arch the one spring to make it sit level.
You need to determine that the frame is indeed straight.
There is a place in Phoenix that does this, so I woud imagine that in big D there would be a couple places that can get it done for you.

Usually, if they can determine that the frame is straight, they would re-arch both. That way, you can tell them what you want your ride height is that you want, and they know by the weight how far to re-arch. I had this done on a '57 T bird, and it came out great.

When I bought an 89 suburban way back when, I noticed that the body had shims where it bolted to the frame, and a small one on that side spring. When I took it back to the dealer for warranty work, the service writer explained that with thousands of springs being manufacturered for each model year, no two springs were exactly alike, and that different vehicles showed signs of spring mismatch even though each spring was not defective, the unequal spring height sometimes caused doors to mis-align. They added different shims to adjust the body/frame assembly.

My 86 corvette has bolts that hold up each side of the car. The usual mod that everybody does is to add longer bolts to the fiberglass springs to drop them down. When I changed my spring bolts, I noticed that tightening them the same made the right hand side about 3/8" low. Upon some research, I found out that some springs were unequal even from side to side. So the fix for that was to adjust the car with a yardstick to the height desired, and then go have the rear end aligned.

How does that help you?
It may be that one spring was arched poorly, and may need adjusting.