The M35 6x6 truck is great if it's what you need. It'll go anywhere (slowly) and will haul 2.5 tons in the bed offroad and 5 tons onroad with the same in a trailer. Has a sturdy, simple drivetrain, and is widely available cheaply (for what it is) in OK to very good condition. There are some downsides:
1) All the "oil change" items tend to be unique to the truck. Example: the air filter is a Donaldson, but it's only used on the 6x6. Parts are, and will be widely avaialble, but aren't as cheap as generic items would be. It's actually cheaper to do an oil/filter change on a 5 ton 6x6 than it is on the deuce-and-a-half, becuase the 5 ton uses generic parts.
2) The bed is dock height. This is great if there is a loading dock on both ends of your drive, decidely not great if there isn't.
3) It's awfully big and heavy. if you don't need to haul 5 tons off road in one go, you probably would be happier with something smaller.
4) it's really a dedicated offroad truck with limited on-road capability. If it's what you want, great, but beware the limitations.
5) ergonomics...there aren't any. My friend wears ear plugs when driving both his M35 and his Cummins-repowered M37 over long distances.
A more practical option might be the mil-spec versions of the Jeep pickup, Chevy pickup/Blazer (CUCV), or Dodge pickup/Ramcharger. All are rated for 1/2 ton offroad (usually double for onroad), have heavy-duty diesels and 4wd. They're spartan, but less-so than the M35, and their drivetrains have civilian relatives, so parts are common and cheap.
The military found them a little light-duty, and wanted a common chassis with a common parts pool, so they were phased out in favor of the HMMWV in its many forms. "A little light-duty" for winning WWIII is probably more than sufficient for your needs...
