Having owned 4 different Ford SUV's, 3 Explorer 1 Expedition, over the last 20 years (94, 98, 00 04) and a few other models (Durango, Grand Cherokee) I have some experience with them. All the Explorers had the 4.0. I do most of my own work on my stuff, but have a good mechanic for stuff I just don't want to do, have never been to a dealer except maybe to buy small parts I can't find online.
I recently sold my 00 Explorer XLT 4.0 and bought a 04 Explorer XLT 4.0. Both had about 90k miles when I bought them. The 00 was the most dependable vehicle I have ever owned, and I have owned 50+. Nothing on it ever broke, was replaced, rebuilt or repaired except normal items like brakes, tires, two batteries. I changed the oil about every 5k miles, that was about it. Never even charged the AC and it was still ice cold when I sold it at 178k miles. Always got right at 20MPG.
I bought the new (to me) 04 Explorer last month, 4.0, 2WD XLT 17" wheels for $5300. Looks like new in and out, silver/gray, tinted windows which you have to have down here in FL. Much bigger and more room inside, much quieter and better ride (independent suspension), and overall just a great looking SUV. Two things I didn't like about it was too much cheap plastic inside and the MPG in city, but fixed the few broken plastic parts and working on the MPG. I've been keeping an accurate measurement and drive easy, city about 15, hwy about 19 - I drive mainly in the city.
Have never had timing chain problems as mentioned above, and really have had very little overall problems with any of them. That's why I keep getting a newer one every 5 years or so.