Rotella T 15w40
In my 02 7.3 I used Rotella T 15w40 changed it every 5,000 miles. The truck never had an oil related issue. I ran that truck 410,000 miles towing 90% of the time.
The truck is still running and has 430,000 miles on it now.
All I can say is "If it works, Don't fix it"
Zilla