Well maintained is a subjective measurement. For some on here that would include rotating the blinker fluid. A simple indicator would be to know if the axles had ever been serviced/repacked within the last 60,000 miles.
Remember that these trucks are 10+ years old. They will require ongoing maintenance. Some stuff will be on the verge of wearing out. You can't blame the truck for that. Comon wear parts at 150,000+ miles include water pumps, U joints, radiators, brakes (not just pads but rotors and calipers), rust, tires, rubber hoses, plastic bits that are supposed to flex but don't now (air cleaner tube), bushings, paint, seat surfaces, shifter knobs, brake & gas pedals, steering wheel cover...
The above is maintenance as they are moving/wear parts. Even the paint (sun, wind, rain, hail, sand, bugs...)
What do you consider major? There is no warranty at this point. Depending on your level of desired maintenance though, you can wind up with a substantial bill for bits here and there.
On the other hand, if you aren't worried about aesthetics at all, change the oil once in a while, lube, gas it and go.