Recently I went on a 3000 mile road trip in my 17 3.6 3.21 QC.
This is Houston - Livingston - Jackson MI - Asheville NC - Leesville VA - Charlotte NC - Pensacola - Houston
Averaged over flats, long grades, and some mountains, often 70 - 80 mpg.
Me, Mrs, pupper, and a bed full of luggage.