Ford has about 1,000 different combinations of coils depending on what truck you have and what it was fitted for. Maybe get a new pair of coils, spec'd the same as the factory ones, and try a different kind of bump stop. Timbren maybe, or maybe the sumosprings. Something that has some give in it and actually uses the springs to compress? Seems on the cheaper side of how to go about it, so maybe go back to stock-ish setup.
Bumpstop spacers would be easy.
Firestone doesn't make this diameter and height with internal bumps.
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