Help with fuel economy

[bomhour]

I just bought a 2010 X35d and contrary to what most folks here are experiencing, my fuel economy stinks with an average of 18 mpg. I have brand new Bridgestone tires, and a new oil change. I added fuel injector cleaner this last weekend. I checked the air filter and it's practically new. What else should i check before my 1100 mile road trip this weekend to help with my crappy fuel economy? My wife mostly drives the car and she goes easy on it. it has massive power according to my weekend excursions. Everything seems to be working correctly and there are no warning lights or anything like that.

Any tips are appreciated.

Thanks,
Adam - Billings, MT