I agree with Chris, here.
Check your tire sidewall. Most of these tires are rated for either 44 psi max, or 51 psi max.
And give yourself some time to be trained by your new car! My mileage started out at 41-43, but now (4000 miles on car), I am cranking out maybe my first 49 mpg tank. My last two tanks have been my best. I think you will see improvement as you learn, with or without high tire pressure. BTW, I have the Dunlop SP31 tires, and use 37 psi. This seems to be a good compromise for me.

Steve

STOP terrorism - Drive a HYBRID

Vehicles:
350 miles a week ------------ 2006 HCH II, Magnetic Pearl, w/NAVI (born on May 25, 2006)
350 miles a month ---------- 2003 Mazda Tribute ES-V6
350 miles a year (for now) - 1986 Mercedes 560SL