I ran the tank dry and filled up with 91 premium along with an octane booster.

I drove the same distance and this time I made the trip (roughly 75 miles) in less than a quarter tank. Which of course could be inaccurate when basing this off of the gas needle gauge.

But at any rate, mostly like having the wrong octane rating in the vehicle or having a very poor gas mixture in the tank could of resulted in bad gas mileage.

After my calculations, I got roughly 18-20mpg on the highway when cruising at 70mph.