Canine.....
Two more cents for ya. I have used Mobil Delvac, Shell Rotella T,
Chevron Delo in many diesels over the years, 5.9 Cummins, 6.2/6.5 Chevrolets, and 6.9/7.3 Internationals, and seen many go high mileage (250k plus). I have two friends at Fairview Ford in San Bernardino, Ca; one a 20 year diesel service/heavy repair tech; the other a 25 year wholesale/heavy duty truck parts man, who say the 6.0 is the first International Harverster diesel that has had a problem with oil aeration (foaming) as Debug suggested. They both told me (longtime friends who don't need to sell me oil!) that the factory Ford powerstrokediesel and Chevron Delo 400 are the only oils, to their knowledge, with the proper anti-aeration additive. I run synthetic in some of my other vehicles, if Navistar said it was best, I would definitely run it in my 6.0 too!!

have a great day!!

Tim