The 6.4 was Fords replacement for the earlier Navistar. It was built by Ford and had so many problems they discontinued it after just a couple years.
Before Navistar Ford used a couple international Harvester engines, the 6.9idi and 7.3idi.



I know the 6.0 and 7.3 were also built as a commercial engine but their electronics and setup was much different than the Ford engines. In general they were lower rpm and higher torque.

The 5.9 Cummins was built to be a tractor motor but when they did not use it for that purpose it was offered as a truck engine. Ford was offered it before Dodge but they declined.

No the 6.4 is an international engine.

I just went down to the Valley yesterday and picked up our 2012 F-250 King Ranch 4x4, with the 6.7L diesel. That truck now has 219K miles on it. She pulled down 17 something mpg doing 70 to 75 (whatever the limit happened to be) on the highway. That was about 360 miles. Dunno what I'm gonna do with it. Have the wife's 2018 F-150 King Ranch, diesel, and my 2018 F-350 diesel. Gonna try to talk to the wife about selling either hers or the 2012 I guess.

Depends. I own an old diesel that gets 5-7k miles a year. Its paid for and runs good.
If I was getting new I would probably buy a gasser.

Diesel is about 50% higher than regular gas right now and I'm afraid that it will stay that high.