For $2000 that's a great deal. The 4.3 is reliable and there aren't any major problems you need to fix preemptively to avoid catastrophe, like Honda timing belts or (certain) Ford spark plugs.
The problems I've seen most frequently on message boards (not that they're extremely common, just most frequently reported) are the fuel injector "spider" leaking (the part in the manifold that feeds the six injectors) and the intake manifold gasket. That, and the fuel pump that seems to go out on a lot of Chevy trucks after a decade or so of service. All of those are pretty obvious if you have them, and if not, don't worry about it!
It would probably be a good idea to do all the 60k maintenance stuff since you just hit 120k, unless you have proof the previous owner did it. If you replace the spark plugs, stick with AC Delco.
Beyond that, there's stuff that wears out on any truck of that age... alternator, ball joints, heater core... if it breaks, fix it, but no need to preemptively do anything.