That truck with that engine has a lot of pattern failures.
1) Leakin gintake gasket -- will either leak coolant internally (most likely) or internally. and in a few cases they will leak vacuum to the crank case and cause a misfire. If it is leaking coolant externally, you can see the coolant slowly seeping out from under the intake jsut behind the water pump. If it is internal the inside of the oil fill cap will be milky looking. if the leak is vacuum, it will have a rough idle and load misfire
2) Oil cooler lines if equipped. They are terrible about leaking. Replace to fix.
3) Heater hose quick connect. They WIL BREAK!!! and they are a pain in the but to replace. Normally they do not jsut break off, they normally have to be hit or the hoses have to be pulled. The threads break off in teh intake. Which mean you have to get it out with a hammer and chisel (and a tap if you are lucky). They make newer style that are made out of a harder corrosion resistant material. This should be replaced if you see "brown sugar" residue around the fitting.
5) The central sequential fuel injection system is prone to small fuel leaks under the upper plenum. The injectors are centrally located with a tube and a poppit valve feeding the cylinder. These poppit valves will slowly leak over time causing a check engine light to illuminate (usually a Bank rich doe or O2 sensor code depending). The fuel pressure regulator is also mounted under the upper planum. This piece is known to leak after a lot of miles. It will dump raw fuel into the engine (usually cylinder 4 or 6) causing a misfire or check engine light (see above reason)
6) Like ALL chevy trucke the steering components (pitman arm, idler arm, tie rod ends, ball joints) need to be checked. With that mileage it is possible (likely) they some of the parts need replacing if they have not already.
7) The front axle disconnect motor goes out fairy often if the truck is used in 4x4 much (of if the trucks runs in a lot of water). The original piece uses a bi-metallic strip but a new style uses a true electric motor. They both fail, and the original bi-metallic is a lot cheaper.
That is all i i can think of off the top of my head. Not tryin to scare ya partner. You asked and i am tellign what i see on a daily basis at my shop. The trucks are GREAT vehicles if they have been taken care of. with those miles you should be able to get another 100k out of it pretty easy if it is in good order. I have seen A LOT of those trucks ragged out, but still on teh road.
Shoot'em close. Less to pick.
They might get my guns, but they'll get the bullets first !