i found this post because I have a 2000 Pontiac Bonneville (full size) car with the 3800 v6 engine and just got 32 mpg on a trip from Boston to NYC, all highway, with cruise engaged at 65 mph, no traffic, with one person in the car. Fantastic mileage I'd say for a ten year old car with 82,000 miles. I keep very accurate records using an iphone app, GasBuddy, and only fill up with full tanks. If I use 87 octane, I average 17.4 mpg in my combined highway/suburban roads commute, and if I step it up to 89 octane, I get 19.6 mpg for the combined hiway/suburban roads of my commute, but the 32 on the hiway just really impressed me.