Well let me see if I can answer some of your questions, most of which are rumors started by Chev/GM, dodge fans. I am going to take what you have written and insert my answers accordingly.
I did a little research on the Excursion and I think the 6.0 would be a risky proposition. Why? I believe that you should do alot more research but do it on Ford sites and not by those who are anti Ford. I have owned every kind of truck by all the different manufacturers and every time I come back to and depend on my Fords, hence the GMC I have for sale in the classifieds.
Perhaps you can get all the gremlins exorcised but I did not do enough investigation to decide one way or the other. When the 6.0 first came out it was lets say problematic, but as with any new engine those problems got taken care of and have not been problems since the second year of production. After all the 6.0 out beat the others in test after test by different car magazines and is still listed as the best engine to replace the 7.3.
I suspect that the 6.0 may be a little more efficient and definitely more power than the 7.3 but I would really have to be convinced it was reliable. The 6.0 was and is still more efficient than the 7.3, but not as reliable. This is the reason the 7.3 got the nickname "Bullet Proof" because of its ability to withstand the pressure of use in all forms. Even the other manufacturers tried to copy it, but Ford holds the patents so for now they cant. But as with Harley Davidson those patents will run out and you will see the same engine in other vehicles. If you want convince talk to those who have them and wont part with them, or those who are searching for them and have trouble finding ones that are wore-out, revampted.
The 6.5 GM motor has some problems but they seem to be well known and fairly easy to sort out. As with all new engines, I dont matter who makes them, the first year or 2 always have problems.
The Excursion chassis is a little more modern and advanced over the previous generation Burb but the Ford is quite a bit more investment. That is because of the fact everything in the Excursion is heavy duty, it is on the 3/4 ton platform or F250 frame, Most parts for it can be taken off an F250, it was made to fill in as a daily driver/soccor dad/travel vehicle but still work like a truck
It also seems like the Ford would be a little more hassle to drive in a non tow situation due to the size difference but I have not really investigated that much. Not any more than a suburban of the same size, in that respect Ford, Chev, GMC, suburbans are identical. The only real difference is as I mentioned above it is a 3/4 ton and can be used as such without any changes. Most of your Chev/GMC suburberbs are only light 1/2 ton or heavy 1/2 tons and some need mods to the suspension. I have a freind who has a Chev Suburb and on the title it says HD 1/2, to get it to do what he wanted he had to make many mods to it, and I dont know of anyone who uses them the way we do who has not made those same changes because like me we cant afford to have 2 or 3 different vehicles and must have 1 that serves all purposes.
Unfortunately Ford no longer makes the Excursion, and this is why they can be so hard to find. I wish they did and so do many of us who own them because with the new upgrades in the F250 series it would be a formatable vehicle and quite popular.
If Ford is so bad how come they did not need no bail out money? How come Ford is the number 1 rated truck for the last 10 years? Why is it those who haul and use there trucks always have the others for general use and keep the Fords to work with? You can look at any company you want phone, power comp, construction, the trucks they have for work are fords and the general use trucks are other manufacturer. I can take you to Hot Shot Truck haulers (trucking over road) that use 1 ton trucks, and the majority of them use Ford F350, 450, 550s and have used others but end up right back with Fords, Why? Look at farms, I can take you to farm after farm and it is Fords for work and the others for general use.
Oh go to Ford.com and see the test done by an independent company on comparison and tell me what you think.