Our little dog would go anywhere. Off roading, fishing, camping. Didn't make any difference. She was there and loved it. If the trail got too rough, she would just get in the back seat and lay down.
I have 2.3 with Ford Tune. I was getting 18.5 , now a little over 18. I drive pretty easy. Will see 16 or so between AZ and California but that is running 85 plus