Can I change the gearing in my 09 4WD to get better mileage?

yes it will but not recomended due to your warrenty you do not want to void it make sure you check with your dealership of your warrnety info before you make any mods to your 09

Did they offer it with taller gears in the first place? Generally , when the vehicle is built , those factors are considered and they try and optimize fuel and power. Better fuel economy can vary on how you drive it, not if it used for work, and remember . You have to change both the front and rear gears, and it will have to be done at a dealer in order to retain your warranty. The savings of a few cents per day will take a long time to pay for the gear change. How bad is your fuel economy? Did you not read the epa ratings on the sticker before buying this truck?

Sure you can. You can gear it higher. Although, being a 4X4, you would have to do both differentials, the front and the rear. You could also have the ECU/PCM reprogrammed for best gas mileage, which would tweak the transmission shift points to a lower engine RPM, although that will discombobulate the fuel mileage vs performance balance. But why would you want to tamper with a 2009 model and risk voiding your warranty?

I agree with Corey. You can definitely change the gears and get better mileage but you need to get it done at your dealership as they are probably the only ones that you can have it done by that won't void your warranty but it'll probably cost you a good chunk of change.