Bob,
Your friend is right about the Powerstroke taking 15qts. of oil. Dad works in the mining business, and they have Chevy and Ford Diesels. I just asked him and he said the PSD takes 15 qts. of 15w-40 motor oil. They run 15-40 in all their diesel pickups. These trucks are driven down into a zinc mine, sometimes as far down as 1200 feet!
Ray Kirby, a member on this forum, has a Ford pickup with the PSD. You may try to get his attention, i'm sure he can help you out a lot more than I can.
Take care,
Tim