If this truck is basically OK keep it. You can do a ton of work vs new. Shoot - didn't look back first if already said but even at low miles the timing chain could be jumping around. Rare to me on this engine but it's nowhere near new either. No clue how but some can jump and jump back on time. That you can test by turning crank bolt one way then the other and see how for you can turn it vs the rotor (think has one) in distributor turns. Also, not sure which ones but a lot of nylon toothed cam gears were used that don't like time never mind miles.
Not the worst to get at or do on a Chev block. You really don't know the real condition till you are looking right at them and by then you are nuts not to toss it. All labor and gasket scraping, parts cheap as things go. If unfamiliar you just go like doing a water pump on this type engine and you are almost done. Just the timing cover and voila, there it is. If it goes there, toss the water pump just for good measure. I like new ones not rebuilt (not always more expensive) but some are an improved design. Pumps are just a metal casting with bearings and seals really. Not these TMK but some the impellers get corroded and plain don't pump well.
Would you be fixing this yourself if you had it in hand or finding your own local better known help? Said already almost all 4.3s I knew and not that many actually ran until body was NG to render the vehicle at large not worth messing with any more. It's a road salt problem where used for ice and snow. Frames, even give out - heck the bridges use steel that gives out too. Some whole states don't allow its use and wish they didn't here either,
T