I had the oil & filter changed in 10/2011. This has been 2 years. Mileage was 44,850.
Engine is a 350 Cummins (8.3L).
It's been in storage.
Currently, has 46,300 miles. A difference of 1,450 miles.
However, every 2 -3 weeks start it up and let it run for 45 minutes to an hour.