6.7's can't take just any 5w-40 either. It must meet the Ford spec and not many of them do. I buy the Valvoline Premium Blue whenever NAPA puts it on sale.
I do 10k OCI on mine, but it's almost all highway miles, just loafing along on the interstate with no towing at all.
I do 10k OCI on mine, but it's almost all highway miles, just loafing along on the interstate with no towing at all.