With the 6.0 a higher cetane diesel fuel will help with keeping the turbo functioning properly.
As far as lube choices my personal experience with 5w-40 were sub-par, it sheared out of grade horribely (low 30wt.) and wear metals were higher that the previously run 15w-40.
I am now and have been a 10w-30 convert for the last 60,000mi. or so. Its roughly half the price of 5w-40 and my UOA's look much better, similar to when I run 15w-40