Front end issues were / are a given.
Something you can do, that requires very little mechanical aptitude. The DSS brace
www.solidsteel.ca
and make sure you have a good set of shocks, and possibly update the track bar to the 03 and newer version, or buy an aftermarket one with a lifetime warranty.
Watch for the obvious stuff, front tires wearing funny indicating bad alignment / ball joints. If there are any mods, make sure they are mild, such as injectors, air filter, exhaust, etc. try to stay away from fueling boxes and such.
Do a fuel pressure test on the lift pump, make sure its working properly, anything less than say 10psi at idle, the LP is junk. Vp44 pumps on the 98 - 02 engines really don't like starving for fuel, and will crap out if run for extended periods of low inlet pressure. FASS is a good, although pricey lift pump, water/air separator system.
If there appears to be excessive oil, or leaks, on 01 and newer, check the breather bottle on the front cover, most guys seem to forget about dumping it. I do mine every 2000 km, and also, wrap that bottle in an old sock or something. The fan will take the crankcase vapours and suck them up, coating the rad in oil mist, and causing dust buildup. The result is overheating, had it happen, didn't get too hot though, and things are still happy as larry. For summer work, I extend the blow by tube down, with some 3/4 heater hose, and tie it off to the sway bar. Letting it vent to atmosphere without the added inconvenience of the bottle.
I have noticed some hassles with fan clutches. Not the greatest unit, Hayden #2842 has an excellent warranty, and gives good service life.
There are other little quirks to these trucks, but beyond what I have mentioned, just look for the obvious. check the front wheel bearings too.
good luck