Help! Poor Fuel Economy '06 4cyl Manual Prerunner

Okay guys, I've read all of the posts regarding this and none are worth a dollar to a dog turd. First off it's not driving habits...period. As mentioned above, I have an 06 Prerunner 2x2 4cyl 5spd w/130k and completely stock. I traded my 4x4 v8 sierra for it a month ago solely for better fuel mileage. But low and behold, I'm only getting slightly better than the seirra if I really baby it, and just as bad as the sierra if I drive 70 or 75 on the highway. And 75% of my driving is the Interstate. So the best I can possible do is 18.5. If I drive it like a normal person I get anywhere from 14 - 16! And this is the dead of winter with no AC of course.

SO what did I get myself into? I'm starting to feel as though I traded for less of a truck for no reason. Is there any hope to get better? Or did my plan to save cash just end up shooting me in the foot?

And oh yeah, the filter is new.

Please help!...Otherwise I may be forced to trade this truck even though I really like it.