consult the people at ford. It really depends on where you live and what you use your truck for. right? Hot weather, lots of towing ya for sure 5 40. my truck really runs best at 10 30. i just ran the 5 40 for the last 2 changes and it was ok but better with the 10 30..... that being said i do run my truck all day everyday, in the Canadian cold and watch every mpg closely and listen to my engine. my wife calls me nuts but it runs better and starts easier.
Ams oil is the way to go. if you can add the fass system. i want one for my next addition to my 6.0 psd