I bought mine used with only 4k miles and it was 2 years old. The only bad part was having to replace the front drive axle on the long side. I own and operate my bike shop and I noticed that the new axle had a redesigned u- joint. I kept the old one in case I need it since Ford does not replace the u-joint but the whole unit. Other than that, I have had to disassemble the locking hubs everytime they need grease. Plus replace the battery after 7 years. The upside is that this truck does not get any worse gas mileage than a regular pickup. The MPG does not care if I am loaded down and towing or running empty. This is mostly due to the transmission "learning" as it goes.
The 4WD is awesome! I like having the option of manually locking the hubs for those bad ice storms. I have seen auto lock systems of all kinds foul up when you need them. The seating is the best. The third row is made for grown ups and is really comfortable.
With recent technology going for the multi displacement (where cylinders not needed for power have the fuel shut off) I hope that someone will look at programming the ECU (brains) on these to do that. I hate that all the shock of seeing these trucks lead to their demise. Suburbans are as low mpg.