Frank,..Have you checked your mileage going steady 70MPH on the interstate? I get 23-24. ..
I have no desire to drive the 2019 GT350 on the Interstate highway. Furthermore, the Atlanta traffic runs about 80 Mph+ when not crawling in a traffic jam (same gas mileage but more fun at 80 Mph).
I must add that gas mileage is not my goal. I am not trying to save the world with my lower carbon usage.
I say go fast and enjoy the experience. The GT350 can get it done.