.
The difficult thing about these low mileage trucks is that they get used. There is a motor-pool sergeant that will not hesitate to stick his boot in your asprin. But the way it works is that the replacement trucks are not generally all replaced at one time. Arbitrarily, ten trucks are replaced and those can sometimes be cannibalized to repair some that were already sidelined. So a few become parts trucks. Some are cobbled together with the replacement parts. Like any other mechanic - there are the good ones and the "slap and go" mechanics. Then some trucks are just ridden hard and put up wet.
But most of all, even the good trucks sit. Then they sit some more and even more. There is no fuel shortage, so trucks sit there with diesel in them growing green crap in the tanks. Gas goes bad. These sidelined trucks sit for years out in the boiling hot or freezing cold. The rubber gets dry and cracks develop. The cab bushings rot, the cute little wiper rings one the cab jack rots away too and water creeps into the system. They might sit in "disposal limbo" for years before going to the auction block.
There are the stupid things that shouldn't happen, but that leaky turret cover or maybe the canvas top on the M939 Series trucks didn't get any sealer applied to them. Leaks cause electrical problems. AND it just has to be said again that the sun is a real killer. For the most part, 8k is nothing. Even 50k or even double that on a truck that is running daily and well maintained is nothing. Sitting for years while the vultures are perched on the hood is where the problems happen.
We have guys in the outfit who will sell you that could easily be driven half way across the country. There are other folks who will buy an auction truck, do a little work and sell it off. It runs, the brakes work, it got a squirt of paint. All in all ready to go, but is that truck ready to drive that far with no problem? I personally have purchased several trucks. It seems to me that every thing that I fix definitely improves my vehicle. I also discover that as I fix "X" chances are that I find "Y" that also needs my attention. Since I am in no hurry, I have been steadily fixing and maybe by the end of winter - my repairs will be complete. Truck has stayed roadworthy throughout the fixing. Mostly because I personally need some sort of reward for the wrench turning... A spin around the block does that for me
If you bought a 1984 convertable (RagTop 5-Ton) and drained the fuel, then changed all the filers and fluids. Then replaced every last piece of rubber on the truck from rubber hoses to rubber seals on the window frames, you might be able to do what you want to do. With a few shakedown runs of 50, then maybe a hundred then double that (miles) - you could start to trust the truck. OR you could talk to the right folks who already do that and make a living that way and jump straight to the test drives.
(by the way, it ain't me!)
There is more, but my brain got tired. If you want more, I am sure the others will pitch in with opinions.