tcane:

If I were you and if I were in TX, I would just run Delo 400 15W-40 year round. If you invest in an oil analysis, you might be surprised by its performance in your diesel. Delo also has a straight 40 and 50 oil, so if high temp s your concern, 40 or 50 might work very well.

Many diesel owners run Mobil 1 15W-50 and that is fine as long as you keep it changed in shorter intervals due to the lower soot handling capacity of the CF oils.

There are just my opinions.