Another reason they told us at Kansas City chrysler training its that the new engines have such a small upper ring land that there is less unburned fuel hence less fuel wash destroying the oil. I think the ring land on a 5.7 is thinner than the upper ring. Makes it a pain in the butt to slide a piston in without breaking the tops of the pistons off.
I still only run 7-10 on mobil 1, and 2500-3k on anything with a carb. The demon get changed whenever it starts to look and smell funny.
Funny thing, Brad Penn dosnt have some stupid "our oil is so good you dont have to change it for 10,000 miles because the melecular bonding agents are held together with micro glue fibers equipped with a non metallic form of kevlar to drastically reduce engine wear at the melecular structure" They just tell ya to change it when needed.....