The VT365 (the 6.0 you speak of) is a topic of hot debate on occasion. This essentially is the infamous 6.0 PowerStroke diesel that Ford wound up buying back in droves, and if I'm not mistaken, sued Navistar over. Some say the VT365 is a good engine that Ford tainted with the tweaks they added, but I personally would not buy one.
As an asthmatic, owning a diesel is not a good idea, for me, period, but even if that were not an issue, I personally would not touch an 04+ diesel, period, but especially Navistar. Navistar built good stuff before 04, mind you, but various issues with electrical, fuel, and emissions systems, as well as massive engine failures have plagued the brand's newer offerings since the 2004-2008+ range. You might check out the threads linked in my sig for more info. Good luck in your search, and welcome to the community!