I am far from an expert and may have missed this in your thread but here is my 2cents
If the shims are facing toward the back it would rotate the axle down, as such the pinion angle may be at the wrong angle to the TC. Again I may be way off but my understanding is shims face forward, rotating axle/ pinion upward. With your lift and shackles it would be 4 degrees.
If you do the search thing you May see more on shims
Which is the correct direction of the shim? I installed the 4* like this- with the wedge facing rear:
The only thing I didn't try was the 4* the opposite direction. I tried 2* both directions, and no difference