Motor oil weight for triton v10

Oldme wrote:
My 2000 Ford V-10 calls for 5W-20

I talked to the dealer about this seemingly exceptionally thin oil a few years back and he said it actually had to do with MPG. Obviously thicker oil requires more power to turn the engine, and he said that Ford as a company needed to hit an aggregate MPG number that because of their SUV and truck biz, was difficult. This thinner than what we all grew up with oil, he says does actually help.

Sounds like a good story...