My first diesel was a 2092 Ford F350, Super Cab 4x4 Power Stroke with the International built 7.3, great truck, great engine. I changed the oil and oil filter every 5000 miles or 6 months, which ever came first. I used several different brands of 15w40 oil, but mostly the MotorCraft oil which was made for Ford by Conoco-Phillips,great oil and always the MotorCraft oil filter. The oil actually stayed fairly clean at 5000 miles or 6 months, being a light brown. I am sure this was due to the absence of the emission control [censored] that the newer diesels have now.
I presently own a 2011 4x4 Ram Laramie Crew Cab with the Cummins. Great truck and great motor. With the emission [censored] on this truck, my oil is black only a few miles later, again because of the over kill of the emission [censored]. I change the oil and oil filter every 5000 miles or 6 months, which ever comes first. I use the Shell Rotella T6, 5w40 synthetic diesel oil with either the Mopar oil filter ( made by Cummins for Mopar) or the Cummins Oil filter.