I run E85 fuel about 99% of the time in my 2009 Sierra. I make a lot of trips between Phoenix and Los Angeles and my MPGs typically run between 15-16. I check my mileage each tankful using the calculator-method. I've tried a few things to see if I can get better mileage, like keeping my highway speed at 65 (vs 75) during one entire trip which kept the RPMs below 2000, but did not increase my mileage at all. I also installed cruise control which helps me, but did nothing for my MPGs. I did install a bed cover which gave me a whopping 1 MPG increase...not much but every bit counts. I'm not a lead-foot and I keep the (still factory) tires at the recommended 35 PSI. I was really shocked to see that keeping my speed limited to 65 did nothing to help with mileage! Could the AFM system be hindering the typical MPG saving techniques?