Before condemning fuel economy, especially in this economy, it is necessary to honestly evaluate both the vehicle and the driver's habits. Driving habits affect the vehicle's economy more than any other factor.
Questions to be asked and answered honestly include whether the vehicle is used on short trips, or frequently started cold. In this winter weather, the colder, denser air will cause the computer to add fuel. This is normal, but if the vehicle is used for short trips, and stored outside, these things will aggravate the drop in economy. Starting out with a heavy throttle foot, then stopping abruptly will seriously reduce economy. Anticipating lights, and maintaining a steady throttle foot will add more to your economy than you think.
Evaluating your vehicle seriously will allow some valid estimates as to whether it needs some work to improve its economy. A set of spark plugs, and a clean set of filters, both air and fuel, will improve its economy, especially if these have not been chenged in the last two years. Word to the wise: these aftermarket air filters intended to add to the engine's ability to breathe may reduce fuel economy, especially if the original filter is restrictive. This is due to the computer's ability to add fuel when it sees extra air, as this is its job. Your economy may improve in this scenario if you use the extra air to improve throttle control. It is very easy to "enjoy" the extra power to the point of reducing the engine's economy potential. If the computer, for example, has illuminated the check engine light, it is a very good possibility that fixing the problem will improve economy. Codes set for a problem do not typically mean that the sensor being replaced will fix an issue. Codes set are for the entire circuit, including the wiring and the computer, not just that sensor. Replacing expensive parts, hoping to fix a problem will certainly not improve economy, unless you get lucky. In this case, since you did not mention any warning lights, and you are beating the worst case scenario for economy, I suspect weather and driver habits as the cause. Though the driver's habits matter here, I suggest trying some light fooot stuff, and trying to anticipate lights. Ray