I have a 2005 Excursion. Bought it used in 2005 with 19k on it.
I am a regular member in the Excursion forum at FTE. The Excursion is all we discuss.
First, the Excursion is a oddball son of the Superduty line. the frame of the Superduties is a two piece. there is the front clip section, from the drivers feet forward, and the rear section. The front frame clip, seats, and EVERYTHING except springs from the dash forward is the same as the Superduty line
The rear frame of the Excursion is a different animal. It uses the same drivetrain and can use the same springs as a Superduty, but has it's own hitch that is only made by Ford. The way the hitches were designed and bolted on changed the maximum tow load from 10000lbs in to 2000 models to 11000lbs in the 2003 models.
So basically, there a lot of aftermarket things that can be gotten for the Excursion that come from the Superduty line.
Things to know:
5.4L came with 4.10 axle ratios
6.8L came with 3.73 or 4.30 axle ratios
7.3 and 6.0 diesels came with 3.73 ratios and a 3 pinion rear axle.
Front axle: Dana 50 all years, models
Rear axle: Ford 10.5 all years/models
The Engineers at Ford Derated the springs and made them lower on the Excursion. This was to improve the ride for Soccermoms and make them low enough to go into a low garage door. Unfortunately, the OEM springs sag badly, especially with diesels. It is not uncommon for the diesels to have less than one inch travel to bumpstop or even riding on the bumpstop after a couple of years.
The fix is to replace them with aftermarket lift spring kits, or, like most folks do, replace with springs from a F250 or 350. That is pretty much what I did to mine. (with some modifications of the springs) The specifics of what to look for in spring type and load rating are in about a hundred threads on FTE.
Once, you take care of the spring situation, some common simple mods:
change to tow mirrors
change windshield wiper blades to oones that are 2 inches longer
add door lights (2004 and 2005)
Change tires to 285/75-16 (33's) with F250 springs or 315/75-16 (35's)if you have 4" or more lift.
Better shocks
Rear sway bar
I you do go the 6.0 route, try for a late 2004 or 2005. Most of the TSB's and recalls were already done in the factory and they are more reliable. 7.3's have less power, but are stone reliableLike was mentioned above, get the maintenance records, run a carfax, and get someone from Ford to do an OASIS check before you buy. . The 2003 and up V-10's just keep going and going with only one major issue. The exhaust header bolts can break and need replacement. It is something that can be replaced by the weekend mechanic. It sounds bad, but in reality, access is fairly easy.
Now for use:
I have towed trailers and boats with vans, trucks, and SUV's. With a family, bar none, the Excursion is my absolute favorite. I do not tow only on road or dirt roads, either. When I get upstate PA or NY, I have scouted out areas that I take my 31 ft travel tralier up to 3 miles deep into the terrain. It does fine off road.
It is only this year that I have started adding recovery gear in case I get stuck. I can truly say it was me that decided to go beyond what the truck could go the two times I got stuck. Pulling over hills, it has the power to do what you want.
On the road, the Excursion is a heavy enough platform that it controls the tow, not the other way around. I have a 6.8L with 4.30 ratio, and I have never found myself without enough power to accellerate up hills pulling 9000lbs. The diesel guys have it even better.
Any way, will it pull your 900lb empty, 6000lb loaded trailer up and down off road hills? Yeah, no sweat, no strain.
Some video search results:
http://www.youtube.com/watch?v=eao475RtmDw
http://www.youtube.com/watch?v=n_2oU9guHBs&feature=related
http://www.youtube.com/watch?v=EWud-u3zUJ0