Love my '03 7.3L Quigley, I've done lots of things to improve the ride over the years including Deaver rear springs and as already mentioned, most recently, Agile off road "RIP"(ride improvement package)
http://agileoffroad.com/wordpress/ride- ... t-package/
both made a huge difference and I am now more than happy driving it daily. I just turned almost 130K on our AK trip this summer, never had any engine problems. Just make sure you go over and know of anything on the rig that needs immediate attention that would affect sale price, aside from shocks, check the ujoints on both shafts, ball joints, tie rods, brakes.....I've since replaced and upgraded all of those things on our rig and would expect if it hasn't been done yet, some or all of those parts will need attention.
Good luck, lots of build threads for some ideas on your interior. Welcome to the addiction!!