G6 GT w/V6: Poor gas mileage

[Quality Guy]

Hello,
I took an 07 G6 GT home from the local dealer overnight, and during my 164 mile round trip commute, noticed worse gas mileage than I get in my 98 Dodge Intrepid with a 3.2 V-6. The G6 has the 3.5 V-6, and is plenty peppy, but I would have thought a car with newer technology and lighter weight, would have a net gain of better highway mileage - despite the slightly larger engine. The government's website reports highway mileage on the G6 GT to be 29 mpg, versus the Intrepid's 26 mpg. I'm going to check the plugs and air filter before returning it this afternoon - but any other ideas?

Thank you in advance,
Tom