Hey everyone, came here surfing for some info on the 6.4s and ended up in a V10 thread, go figure. I have a 2000 excursion with the v10. Yes, there is an issue with the earlier ones like mine, where they may shoot the spark plugs out of the heads if they're not torqued down properly, because there are too few threads in the head. This, as it was posted was fixed in 02. The 3v heads have the opposite problem, their spark plug design has a long sleeve that in the earlier ones (05-07) can get stuck in the head when removing it. This problem is better known and documented on the 5.4s of that era.
I've changed my own spark plugs ~10k miles ago, and no issues yet.
As far as performance, it's the best gasser you can buy, hands down. Here's a very good article on these; and the results are very typical. It won't win many drag races, but i'll outpull any other gasser out there...
PickupTruck.Com - Part 3: 2007 PickupTruck.com Heavy Duty Shootout
The most interesting part, probably the diesel vs gas comparisson for each brand's offering:
Basically, it's the gasser that comes closest to a diesel, but it's no diesel.
As far as mileage goes, it depends a lot on the driver. When I switch vehicles in the fall and start daily driving my excursion, I usually get in the 10mpg range around town and 15hwy. I slowly get more and more used to driving it and will hit 12.5mpg city; gotta drive it a bit like a grandpa vehicle, but it is possible to get ok mileage out of them. Yes, 12.5 isn't anything to brag about, but compared to my old f150 or just about any gasser, it's not that bad. Doing it on 87 octane with 15 dollar oil changes, and 10 dollar fuel filters doesn't hurt either.