Regular maintenance will keep these things running forever, but they can get expensive when they break...but at least its a Chevy/GMC, so it's not too bad. Plus these things are relatively easy to work on compared to new cars...so a lot of us do our own work and just buy parts. A basic recommendation is to use AC Delco parts...some guys prefer other performance parts, but you can never go wrong with AC Delco.
Big recommendation - regular oil changes will do wonders for you!! When you buy your ride, see if they know the maintenance schedule and how recently it was tuned-up. If the tune-up is due, buy the parts and do the tuneup. Personally, I always change just about every fluid whenever I buy a used car - oil, coolant, power steering, brake, trans, diff.
If you venture into the world of trans and diff fluid, definitely do your research and DON'T FLUSH those systems, just remove and replace. For old coolant, FLUSH this out, especially if the truck is running DexCool Coolant (all '96+ have DexCool)
I don't have it in front of me, but there is a thread in the OBS forum that identifies all of the parts that need maintenance - tuneup, fluids, etc.
One part commonly overlooked - grease your front bearings!! It takes <5min, but you will need a grease gun and auto grease.
Hope this helps!
