Just a note on the Firestone air spring kits for trucks.
As far as I know they don't make a full air suspension kit for pickup sized trucks. What they do offer is air helper springs. They allow you to put air in them to carry more weight, or to level your truck with the same weight you normally carry, but they will not improve your empty ride unless you loose some of your original springs and rely on the air springs for the weight capacity.
At
http://www.keldermanairride.com/index.php they offer many different kinds of air suspension kits, some that use air springs to smooth out the ride but retain your leaves, some that replace the leaves all together.
