Go to Superduty Headquarters online and check out the Edge lift. When ready, call them and ask for Ryan.
Get the Edge 3.5" lift. Lifts the front slightly, levels the rear. Uses Bilstein shocks.
I just did this to my 2003 Excursion. I'm very, very pleased with the outcome. Completely improved the ride...and leveled things out. Cost apx. $1,500 for parts, and apx. $400 for install at my local service place.
I am installing rear airbags on the X, as it has apx. 2" sag whent he boat's hooked up.