About 7 years ago, I ran Wild Horses 10 pack rear leaf springs. When they were brand new my Bronco sat a hair high in the back unloaded, then leveled out with a fairly light weekend trail load, like I felt it should (no hard top). I am not exaggerating, after eight weekend trail runs, those springs sagged out where my Bronco sat two inches lower in the back with the Bronco unloaded.
I called Wild Horses and they told me I had to bring my Bronco down to their shop for them to decide whether they were going to help me or not with the issue.
I didn't get the feeling after that phone call that they were really that interested in helping me, and the cost of losing a days worth of wages to drive down there without a guarantee of them fixing the problem was not worth it to me.
I cut my losses and took the springs out and put F-150 leafs in. I gave the sagged out 5 1/2's to my buddy that has a 3" suspension lift. The sagged out leafs are currently under my buddy's Bronco with the 3" lift and his rig sits perfect in the back.
* granted my springs were not stock height, but that is my experiece with WH 10 pack leaf springs*