My 2018 SS (just hit 400 miles yesterday) avg 23.6 mpg over an 80 mile quick road trip on the Turnpike. Six speed manual. Was cruising between 72-75mph. Did some back country driving too. I did see a high of 28mpg briefly...but MPG is not a consideration when I bought it...but it does get better than expected! My grin and overall happiness in the car is a larger factor
Lee