Stupid question...do the splash guards decrease the mpg when driven at highway spped? I am on the Interstate a lot at 75 mph for 20 + miles each way to town. With E-85 we were seeing 14.1 mpg, after switching back to Regular, we are seeing 21+ on a 2013 V6. I have the splash guards, but have been reluctant to install them, do to the possible increase in drag. Am I over thinking this?