Get a 4 cylinder? Technically there is nothing wrong with your gas mileage being 17mpg. That is on the HIGH end of what those engines in those trucks got. Take the tips I suggested, and some from the site 1BAD80 posted . . and you might gain a gallon or two. Short of that, get a little CRX or something to do your daily driving in.
Personally if I had a car that was supposed to average 16mpg and I was getting 17 Id consider myself somewhat lucky