For my personal vehicle....I like to use a blend of conventional HD Diesel oil, rated CJ-4, SM, and synthetic PCMO for the summer heat.
The blended mix is 2/3 HD Motor Oil and 1/3 synthetic motor oil in 0w,5w-20. I find that the engine seems to run much smoother with this mix....only in the summer.
For the winter....I'll run conventional or synthetic motor oil.
Now I'm running a blend of 2/3 Mobil 1, EP, 5w-20 and 1/3 Mobil 1 15w50.