There's guys running 100% in some IH buses in Mexico. Whatever bio is used on a 12 valve cummins is pretty equal on the 466.
MPG is extremely variable on a big truck. With highway gears, overdrive, a light truck, and a light right foot, you may see 13, or even 15. The one I use a work gets 5.7mpg. But it's 28k pounds & has 4.78 gears & no overdrive.