Anybody using synthetic oil? Help with MPG? etc.

I see a few tenths empty and towing, like .1-.3 mpg. I can make more of a difference lowering the cruise 3 mph. Towing I prefer the syn as high air temps with mountains and large trailer tends to really hit the dino oil hard.
Changing the diff and transfercase to syn were another .1-.3 mpg.
A single 0-70 WOT run down a onramp can shift the tank mpg by almost .1 mpg.