Hino only has 11% of the Class 5-6 market. The dealerships for them are also almost always dealers of more common brands, so most of the effort is put into training the mechanics for the other brands.
Most of the issues with these trucks stems from a lack of people qualified to work on them. When the truck has had all of the computer updates done and a few notable discrepancies addressed, they run for a long, long time. One guy on here has 750k on his, another member here has around 600k, and I regularly see them appear at the shop with 300k-700k and still running every day. The ones that blow up have either been horribly abused, have had idiots work on them, or do not get maintained much at all or have obvious problems ignored.
The DT466 engines use a high pressure oil pump to compound fuel pressure in the fuel injectors. This means that they do not like having their oil changed at extended intervals. And the age of these trucks means that a lot of the seals in the engines are getting older, so you start seeing symptoms of internal high pressure oil leaks. Things like being hard to start when cold. Or hot. Or engine oil going into the fuel tank. Or stalling. Fun stuff like that. Pinpointing the problem can be a hassle.
You mean an Isuzu FTR/FRR? Not bad. Fun to drive. A little tiresome on long trips. Eventually you will have engine oil go into the cooling system. Figuring out whether the oil cooler or head gasket is leaking is impossible without eliminating one or the other first. Engine parts are not cheap. When one of these starts going south and acting dumb, it at least does it slowly so you can recognize it before it scatters parts all over the interstate.
The point I'm trying to make is to realize none are perfect, all will eventually end up with a multi-thousand dollar repair bill, and there's no guarantee of anything. So you need to figure out who your local truck dealers are and find out from their customers if they are crooks or not. If you find a good shop, buy a truck from them or at least have them inspect whatever it is that you're planning on buying. If you're buying from a private party, make the sale contingent on it 'passing' an inspection by this shop. Some sort of plan like this can save you from making a terrible decision.