Years ago a chemist friend warned me about ethanol gas for cars. He claimed it cut gas mileage far more than the price justified. Starting out from Casper with a tailwind, I averaged close to 27 mpg, filled up with regular gas and continued to enjoy over 24 mpg to South Dakota, where one's choices are ethanol or ethanol. Slowly but surely the mpg began to go down as we traveled farther east. One factor to also consider is we dropped over 2,000 feet in elevation.
Sometimes things aren't always as good as they are supposed to be.