I have used over 200+ gallons of E85 in my 06 suburban that is a flex vehicle. and the milage drops by ~1/3 to ~1/2.
15 to 22 with regular and 7 to 15 with E85. Pulling a trailer it goes down to 7mph verses 15-18.
Kept hoping it was a fluke, the weather changes, etc. Power and accelaration stinks also.
With the current price difference of 10-20% I will not use it anymore unless the price delta is 50%.

My old 69 Camero 302Z was 4-6MPH light to light.
A set of slicks lasted one night at the strip at best.
Less than a month of street use. Trying to decide what type of hot rod to build around the engine.
Wish I never sold the body.