I did a bunch of research on these engines when I was thinking of buying one. The main thing is regular oil changes, its oil pressure from the High Pressure Oil Pump that actually opens the injectors. The reservoir where this oil resides doesn't cycle through the filter as regularly as the stuff in the oilpan. As with any diesel make sure you are around to hear it start when cold.
Another common issue with the powerstrokes is the wiring harness that goes into the valve covers. It tends to deteriorate and break. The truck may have low milage, but it has been around for a while, so age plays a part.
Beware of any aftermarket performance done to the truck. Some chip installations tap directly into the wiring of the truck's computer system and depending on the quality of the install, they can actually cause more long term damage than the short term performance boost most get with them.
Other than that, its the typical standard used truck inspection, leaks, worn parts. rust, bad body or wheel alignment etc.
One last thing, if you test drive it, drive the hell out of the truck if something is going to break you will find out then and before you buy it. Its a good way to find band-aid jobs people put on just to sell the vehicle.
