Hey, Here is a post from another board I posted. Some of it may apply to your case. It is a bit wordy though. Good advice above, for sure.
"Don't know much about gas trucks, BUT a couple of things you could possibly do to increase your fuel mileage (every little bit helps). Check out this link, granted he spent a bunch of dough, but there were some small things that made a bit of a difference: (yes he is annoying and it is a bit goofy, but the ideas might help)
http://www.spike.com/full-episodes/288b ... n-3-ep-523
You are not going to be running a 30+ mpg truck w/o a diesel (IMO), but if you were at 19 or 20 that might be a bit more respectable. I will try and rate them in order of easiness:
drive slower (This one might actually be the hardest to do!)
keep the a/c off
keep the excess vehicle weight down - maybe take that cinder block out of the back
see if there are any tuners (or chips) for your truck to increase fuel economy
new exhaust and/or intake
electric fans instead of a engine driven fan
freewheeling front hubs - reduce engine drag
Go back to stock tires - or, as mentioned above, re-gear maybe
Lower wind resistance - no rack etc..."
Good luck. 10 mpg is tough.