My 98' lemon had three genuine ford replacements because of sag. I made my own extended shackles, it pretty hard to get Explorer bits in Australia, They made a great short term lift and took away the rear droop. BUT, after three months the leaf springs just kept sagging. Finally my local dealer decided to send the springs to a local spring works a they did an add a leaf under warranty. This seemed really cool but that made the car jump all over the road. just a word of advice after suffering months of torture here. The back end must ride lower than the front. So if you put extended shackles in wind those torsion bars up so the front sits slightly higher. I don't know why but sure as hell you'll feel the back end jump across the road when you hit a slight bump on a bend if you don't. Then again my old truck was a real lemon. Reputable add a leafs made do ok.
Best of Luck
Paul Golby