I just took a 1500 mile road trip from Arizona to Iowa in the 500 rwhp supercharged 6 speed gxp and averaged 23 miles per gallon per tank full. My cruise control was set between 74 and 79 depending on the speed limit at the time. I did 16 hours on the second leg of the journey. I have to say these G8's are extremely comfortable. I have to laugh because I get more mpg than the original purchase window sticker, yet I had to pay a gas guzzler tax.