If 4WD look to see if it has been converted to Manual Lock/unlock Hubs, none of the Ford Auto hubs worked well after a few years of use.
4.0l engine, 1990-2000 was a good solid engine, reasonable power, expect 16-18mpg
3.0l "Vulcan" engine, 1991 to 2008, was also a good engine but lacked the power of the 4.0l and got about the same MPG, nothing wrong with it but if you are choosing between the two go for 4.0l.
2.3l or 2.5l "Lima" engine, is another reliable engine, but does need the timing belt to be changed every 70-80k, it is a 4 cylinder so not a power house but did get good MPG above 20, so a popular engine choice for small pickup truck, although 4WD option would be few a far between.
Drive trains were good on all models, manual trans is preferred by most because of the large chunk of cash($2,000-$2,500) needed for automatic rebuilds, but long term changing the clutch a few times on a manual will cost the same if done in a shop.
Thing is that most can do a clutch swap themselves but not an automatic rebuild, so......
Frame(and body) rust is an issue on all vehicles, so worth having a look, rear spring hangers tend to go first.
Look for non-factory wiring, when a vehicle get 15+ years old it could have had a few owners, and each may have added things that could cause you issues down the road
And NEVER EVER buy a vehicle that doesn't have a Check Engine Light(CEL) come on when key is first turned on.
"Just a burned out bulb"................in a pig's eye, lol.
And if CEL is on while driving, it is NOT a "simple fix", if it was they would have fixed it, they are selling it after all, right.