hey you guys with bad fuel consumption,
If you havent changed your air filter or fuel filter in a while those are the two major things that cause that. Also If you have old spark plugs the fuel is not getting burned all the way. On my 99 3.5 I just had a TPS take a ****, that will cause a check engine light and the Idle will go up, wich in turn uses more gas. The CEL wont be on all the time, but goes on and off. So you may have a bad TPS and not know it if theres no light.. If you have a loss of power with the low milage you should take a look at your CAT if its plugged you loose the majority of power and milage drops. I doubt your o2 is cusing the problem if you have no faults for it. If there are faults for it, it will tell the computer to go to like a "default" type mode and just dump in extra fuel so you dont run lean and burn **** up, but i would look at the most obvious things first before you go and drop a couple bills on a new one for noe reason. Also the higher miles you get on the truck, the less it will get. after market cold air intakes help alot. You usually see a 2-3 mpg gain.