My '93 Ranger 4X4, with a 4.0L-OHV, 5spd, 3.73 gears, and 265/75/15 tires, gets about 16.5mpg, on average, with a mix of in-town and highway (more highway though). At the end of last summer, I got nearly 18mpg on one or two tanks. Over the winter, I saw a few as low as 15mpg, but that was with a lot of idle time, to warm it up, and a lot of crawling in snow-storm traffic.
Also keep in mind that most of the time this truck is hauling scrap metal, so there is usually a lot of weight in it. I also have stomped a foot shaped crater in the driver side floor, right under the gas pedal. (not really, I'm just trying to be funny)