SUPPOSEDLY, Ford fixed the spark plug problem on the Triton engine series (4.6L V8, 5.4L V8, and 6.8L V10) starting with the 2003 model year.
There was a larger component to the problem than the plug extending into the combustion chamber; the real problem was that Ford only put about seven threads to hold the plug into the roof of the combustion chamber. They only threaded about half, if that, of the thickness of the combustion chamber roof. The heads are, of course, aluminum.
So what happened is that the aluminum gets hot, it's soft to start with, and with only seven threads there, the plugs start to back out a little. Heat seeps up into the threads, further softening and loosening, allowing the plug to back out even more, until finally the force of combustion blows the plug right out of the head, trashing the threads and destroying the coil-on-ignition pack that is on each plug.
How do I know? I had a 2001 Excursion with the V10 that did this. Ford would not back it, either.
There is a company called Time-Sert that makes a repair kit to fix this problem. It is that common. The repair is an insert that looks much like an upside down top hat, that is made out of high strength steel. What you do is drill out the old threads and enlarge the hole to a much bigger diameter. You then tap the new hole for the ENTIRE depth of the combustion chamber roof, so you have 15-20 threads now holding it, instead of 7, and the diameter is three times as big. So you have fantastic gripping force now. OK, so you then apply permanent lok-tite to the insert and run it into the newly drilled and tapped hole and torque it to 20 ft-lbs. The inside of this insert is exactly the contour of the original combustion chamber spark plug hole, so you can use the original plugs. Last step, you run this mandrel through the newly installed insert, and it swells the "head" of the insert on the inside of the combustion chamber, like a rivet. So there is no way in the world it is ever coming out. This is the correct repair.
I have this kit, and a few extra inserts. So if you buy the Ford and it blows up, I can fix it for you cheap. The inserts themselves are about $9 each. The kit cost about $400, because of the special tooling that had to be made to allow a guy to do this repair with the engine still in the vehicle.
Oh yeah, on a Super Duty Ford, you have to pull the engine to get the head off; there isn't room to remove the head with the engine still in the truck. And, you cannot simply pull the engine out through the hood. There isn't room. You have two choices: (A) unbolt the front suspension and the front cross member and drop the engine out the bottom, or (B) undo the body bolts, wiring, linkages, etc., and lift the body off the frame and set it somewhere. Then you can get the engine out.
The 5.4 V8's were notorious for blowing the passenger side rearmost plug. The V10's would blow either that one or the one just in front. Mine blew the one just in front of the rear most passenger side plug.
I liked the Excursion a lot. It was a really nice vehicle, and it towed very nicely. But after it blew up like that and Ford told me to pound sand, I fixed it myself and got rid of it.
I bought a new Dodge Ram with the Cummins turbo diesel and never looked back. All I do now is turn the key and drive.
Truthfully, I think you should look hard at a Dodge with the Cummins. They are hard to beat. The trucks may not be quite as fancy as the Ford's, but you don't have much trouble with them, the Cummins is stout as all get out and will outlast any of the other diesels (much less a gasser), and they get good mileage to boot. As well, all the tranny issues I've ever heard of with Dodge's have been with the half ton models. I know a lot of guys with the 3/4 ton diesels with automatics and none of them have ever had a transmission problem (at least not before they modified their Cummins engine to make 800hp and 1500
ft-lb of torque....but all bets are off once you start doing that...have to call ATS and have them build you a super tranny at that level....)
Oh yeah, my first car was a '72 Dodge Polara with the 360 V8 (5.9L...should be the same engine as in this truck you're looking at). It had 274,000 miles on it when the thrust bearing finally wore out. It never did blow up, but she was using a lot of oil at that point. The 360 is a good engine; they built it forever (it started as the 273, got enlarged to the 318, then the 360). It'd probably do you OK. But you can't beat a diesel for towing.
Anyway, best of luck. If you want a Ford, I'd say get a Powerstroke. Otherwise, get a Dodge.