use NON Ethanol gas ad it will climb back up a few mpgs
i run 87 octane non ethanol and its like night and day compared to running 91 octane that may contain 10% ethanol
but towing mpg will drop based on tons of variables....
wind, right foot application, speed, frontal area of trailer, weight of trailer, temps outside, a/c on fresh vice recirc,
i just towed a tad over 6500lbs of rock on a flat bed and it only dropped a small fraction to 16mpg