XJ/MJ rear lift pack flex issue

My daughter decided she wanted a larger lift on her XJ ( 3" to 4.5" )
So I took a main XJ leaf and an old set of MJ leafs and made up a pack.
I used 3 XJ leafs and the three MJ leafs and got a good 4.5" lift.
The problem is it doesnt flex worth a hoot out back. I figure I might have a few to many leafs out there but before I tear it apart again I wanted to ask If anyone else is running a setup like this and how does it flex on yours?.

I was thinking about going to 4 leafs instead of 6 and useing MJ shackles to keep the height , does this sound like it will work?

The MJ are SUA as I am sure you know but mixing the much longer leafs with the XJ ones would cause a harsh arch that needs to be overcome when flexing (reversing the arch). The MJ shackle would help, try swiching an MJ leaf with another XJ leaf. Other thoughts are painting with a friction reducing paint and adding friction reduction pads between the leafs. Good luck.