A friend of mine bought a 2001 SuperCrew 5.4L 4WD model a few months back with around 90,000 miles on it. No complaints so far from him. He loves the truck.
My cousin had a 1999 Super Cab 4WD with the 5.4L. I can't remember how many miles it had when he sold it, but he had it a few years and he drives 30,000+ miles a year. This truck was used as a work truck. There were no mechanical issues with the truck, but there were some issues with the body. The rear window leaked when it rained...pretty bad too. Some interior panels broke as well. The truck was worked pretty hard. He had bought two 4.2L F-150s prior to this one that were excellent trucks. One was totalled by a drunk driver, but the other one racked up somewhere around 200,000 miles by the time it was sold. Both he and his wife say that their 1998 F-150 4.2L was their second favorite vehicle (their 1998 Mustang was their most favorite).
Personally, I really like these trucks. They would be my first consideration if I was looking for a 1/2 ton. The transmissions may not last as long in this application, but you see automatics fail in a lot of full size trucks across the board. The 4L60E and Dodge transmissions don't exactly have the greatest track records in 1/2 ton trucks either. They have to move around very heavy vehicles and they just don't take well to abuse or lack of maintenance when they are already doing more work than most automatics. If you look at how transmission like the 4L60E and 4R70W do in smaller applications, like Blazers and Explorers, they last a very long time on average. I bet with a trans cooler and half decent maintenance these transmissions can last plenty long in a 1/2 ton.