F-150 Mileage

I have a 2005 F-150 XLT 5.4 liter with a 3.73 rear end ratio and 9800 miles. I purchased it new in July 2005. It gets 18 mpg on the interstate, but only gets 8 mpg consistantly in town. I am really disappointed. Is this normal, or could I have a problem that can be fixed?

Are your trips in town short, by that I mean no longer than 15-20 mins. of run time. If so it could be that your engine is not warming up to proper temps. If your egr system, and all the other systems are not getting up to temps. your mileage would be effected. Also alot of idling at stop lights and in and out of stores is a real gas guzzler. 18 highway sounds about right. Try to see how long your truck idles and try to conserve your trips around town and I think your mileage should improve. I know this is not very fiesable, in this day and age but any little bit would help.