Small update: I used Renewable Lubricants' 5w40 Low Ash Diesel Oil with an Amsoil EaO filter on the 6.5 Diesel and had no problems.
I only used it a little over 2k miles over a 6 to 7 month period however. Still, considering I took some of the unused oil and poured it on the ground and the grass regrew within a week it could be useful depending on your application. As for fuel efficiency this particular 5w40 is on the thin side (closer to a 0w40 than a 5w40) so if you switch to this you may see a MPG gain if you were using a thicker oil. Below I have linked the data sheet for this oil and their thicker Diesel 5w40 oil so you could check their viscosities: