Steel has somewhat of a memory. It wants to return to the shape it was before. Having the springs tempered after rearched my help, but even then it is still just a matter of time before they sag again. Even aftermarket lifted springs sag a little after time and use.
87' Samurai, 5.5" SPOA, 2" longer shackles, Modified CJ-5/Samurai springs, 31x10.5-15's, Hi-lift jack, everything else pretty much bone stock.