@lil_Blue_Ford :
OK, has you have noticed when you go from spring over to spring under, you must account for the thickness of the spring pack (1-1/2 to 1-3/4" depending on which model/payload package you have).
The other one, which you noted at start, was Ranger axle isn't in the middle of the spring, but closer to front (~25" from front/~30" to rear). Part 2 is the axle
is almost in the middle, so the "effect" of longer shackle is reduce. If it was exactly in the middle, if you made rear shackle 3" longer than stock it wound raise the truck 1-1/2", but due to the differences in fore/aft lengths, it only raised the truck 1-1/4"*. Which is why DJM lowering rear shackles are significantly longer than stock ones. And they're just trying to limit the amount of lowering, not put a 4x4 back to approximately stock height...
*My dimensions on spring length were off by a little so I didn't have to go into 1/128ths for amount raised.
Next problem:
We'll skip the theoretical and go directly to your issue.
You have built up a spring from a number of leaves others. So, the leaves weren't manufactured with mating curvatures. Also, as you have shortened leaves, they also don't thin at ends like leaves did from factory.
When you assemble the leaves, you are able to preload the leaves, so it looks correct. But as you can see when your load the springs the wrong curvature of the lower leaves isn't pushing continuously against the top leaf, but concentrating its force at end. Which is making the top leaf do funky things. That stress concentration is also bad for longevity of the leaf - it will fatigue and break there.
As it is behind axle, it will just let you down at some point (pun intended).
I'd like to see front as well. If main leaf breaks in front, it dangerous to rest of us on road with you.