You can lower the back of the 2500HD about 2 inches by using a longer shackle. This will not affect the load capacity. DJM Suspension the longer shackle: http://www.truckshop.com/product.php?productid=17829.

If you want more drop than that, DJM also makes a 3" front 5" rear kit, and a 6" front 8" rear kit.