The Ford 6.0 has a bad rep but as you noted they can be fixed and there are a lot of 6.0 owners that never had any of the problems. That being said I'd still avoid them if you can find something else in your price range.
Diesels hold their value, that's good if you own one, not so good for you. You will also find that duallys are rare beasts on the used market. You may have to search far away from where you live. I'm sure you are aware of the dangers of EBay when buying vehicles. If not be very very careful. You certainly want to take whatever you find into a diesel mechanic to look at before signing the paperwork. I'd be looking for an older Ram. Or and older Ford 7.3