I have a ecoboost platinum 3.31 rear end completely stock. I get 11.5 mpg average in town and 15 mpg on the highway. My friend with the 3.73 gets about the same, a hair better but another friend with 3.55 averages 19 on the highway and has gotten up to 21mpg.

Wondering if anybody else has been having the same results, trying to figure out the best rear end. All driving is moderate and highway is at 70 mph.

Also if I drive about 45mph without stopping I can get about 22mpg.

 

As you have noticed by this time , there is a miles per gallon penalty for speed over 55 MPH and ecoboost can't help you there. If I'm not mistaken the whole thing of an ecoboost engine was to deliver the power of an 8 with a 6 , mpg a crapshoot !