My oil history:
-- Swapped factory lube for Rotella @ 1500 mi. (break in crud out)
-- Changed to Delo 400 from 5K to 12K. Didn't like smell of Rotella
-- Tried Redline 15-40 based on my good experience with their other oils. Like it a LOT, but too expensive.
-- Switched to Valvoline PB extreme. Engine didn't like it much.
-- Switched back to Delo.
-- Decided that I never want to run a 15-40 (too thick). Bought some Rotella 10w-30 (CI-4 rated).
From here on out, it's a 30W oil-- I'd buy a 0w-30 if they made one, but 5 or 10-30 is what I'm going to have to run.
I like Delo 400-- wish they made a 10-30, so I'm stuck with Rotella, Redline, or RP.
If I towed heavy or lived in a hot climate, I'd consider a 40wt again. But in my usage, it's too thick-- my average oil temp is pretty low.
EDIT: there was some M1 T&SUV in there somewhere too. .
jlh