I LOVE some Rotella T6 15w40...
That being said, tuner recommended Motul 5w40 xcess2 for winter and said I could run the T6 15w40 in the summer.
I am currently running Xcess2 right now. It's oil.
Edit: used to be an Amsoil dealer and run it in everything. I didn't have any issues, just cheaper for T6 and I like it. Now Motul in the winter so my tuner doesn't cry foul...