While driving style does have a huge effect on mpg it's not always how you drive it. When I was young I owned quite a few Chevy's and some got fairly good mileage while others didn't. One I had in particular, a 74 Monte Carlo with a 350 2 barrel got terrible mileage (7-9) no matter how easy I drove it. It ran great and had 3.08 gears so it wasn't spinning hard or laboring, just a smog era inefficient engine. I added a Comp 260 cam, dual plane intake with a 650 vac sec carb, and dual exhaust with better stock manifolds (ram horns) and the mileage over doubled. So did the power