I have a 2006 3.0 with an automatic gearbox. One thing to bear in mind is that they are not as economical as the manual, I will typically average mid to high 20's on my low speed commute and low 30's if I'm doing a dual carriage type commute. I've never seen 40mpg.
That said I run a cold air intake on mine for a little extra noise as I found the engine a little to civilized after having an ///M, I'm not sure if that will keep my mpg down a little or not.