I don't track mileage. I have to have gas so I pump non-ethanol 89 and go. My mods are for performance. Usually though, if efficiency is increased, so is the potential
for better mileage--if one's throttle habits don't ruin it. My truck is
running stronger after about 45 miles of ECU "relearning" (by my notoriously unreliable butt dyno) and I continue to be happy with the intake system.
I recently read here that someone thought the Air Grabber might be a detrimental heat trap. Looking at my engine bay with the Air Grabber, that seems unlikely, especially since the factory Hemi engine cover is gone (which does
look like a heat trap). That's my story. YMMV