Don't let CaryT scare you. He is the resident expert, pretty much, when it comes to the X and its suspension. He has spent a lot of time and money figuring out how to make the X handle like a dream. With that said, what some of the mods can be dont slowly as to not break the bank. I have an 04, in sig, that is not quite how I want it yet, but is still a very reliable vehicle that I tow with regularly. The bump you felt could have been sway bar links, bushings, shocks, etc. I have no experience with lifted vehicles either, but those are the usual suspects for that. You also need to take into account how many miles are on a used vehicle, are those suspect parts nearing the end of their life, etc.
Personnaly I would be more concerned with how the engine is, and the drive train. The suspension can be done at your liesure. If you can find an X with a 7.3 that is not run into the ground, great. If you are looking at a 6.0, you need to educate yourself on some of the engines shortfalls, and more importantly how to correct or overcome those issues. I bought my X with 99,000 on her and just turned 127,000. I have replaced the ball joints, shocks, rotors, brakes, FICM, ICP sensor, alternator, batteries, EGR delete, and a couple other odds and ends. While this looks like a lot in 2 years, I expected it with a 3/4 ton truck with 100,000 miles. What I am getting at is know what you are getting yourself into with any used vehicle, and any known issues that a particular power plant might have.
I love my Excursion, keep it well maintained, and she takes care of me when I need her. Hope this helps some. If you have any more specific, just ask. There are a lot of very helpful people on the ORG.
2004 Excursion Limited, 194,000 miles,
Edge CTS (Gauges only), ZooDad, Turbo Timer, DieselSite Coolant Filter,
RCD EGR delete, CCV reroute, Amsoil By-pass Filter, FireStone RideRite Air Springs,
FICM from Ed with Atlas 40 tune, No Kitty, FPR Blue Spring, DC XP270 Alternator