I've been asked this question via PM.
If the fan clutch is indeed working normally (and you'll definitely hear it cycle on and off), then that's good, a bad fan clutch will certainly cause an overheat.
When the thermostat was replaced, was the little tickler valve oriented at the very top? It's supposed to allow any air bubbles to escape from the thermostat housing and go to the radiator. Air pockets in the system will cause all sorts of dumb symptoms.
Now, onto the radiator. They can seem deceptively clean. Realistically, unbolt the condenser and move it out of the way (lines can stay attached), remove the intercooler (the bolts like to corrode, so avoid breaking them), and get a good look at the radiator.
You might end up with this scenario.
http://i.imgur.com/fwA8JBs.png
http://i.imgur.com/ltrXqGs.png
Another question: What coolant are you running? We've seen trucks come in with a mixture of god-knows-what in the cooling system. Hinos don't appear to be all that particular with what's run in them. They don't have normal wet liners, so they don't need additives to prevent liner pitting. They don't have copper in the cooling system, so they don't need the complex list of ingredients in green antifreeze. I'm not sure what the best easy to get solution is, but a HOAT coolant is what's supposed to go in them. If there's a questionable mix in there, I would drain it all (including at the block drain, located at the front of the oil cooler), add a couple jugs of your favorite flush solution, top it off with water, run it least half an hour after the temp gauge reaches the normal mark, then drain it all and refill with water and run it again, until hot, plus half an hour.
No one likes buying coolant that's a 50/50 mix. But when you get that, the water isn't from the tap, it's distilled and deionized. At the very least, stop buy the grocery store and get 4 gallons of distilled water.
We've seen no issues when running the Hino coolant, either the pink or the blue stuff. Pink goes in everything up to '11, blue goes into 11-14 conventionals. Pink goes in all new cabovers. I forget which is which, but one is good for 300k miles, and the other for 600k miles.