I just filled up and checked mine. Not so hot here either but not as bad as yours. I got 15mpg on my last fill. Stats 04 Hemi QC 2x4 ran on 87. I have no mods all stock. I'm going to try 89 next and see what happens. As that is recommended though the manual states 87-89.

 

If it makes you feel any better, my wifes Acura RSX gets 18 mpg in town, but stretch it's legs on a road trip of even 30 miles, and that goes up to 27 mpg. Cars in general, especially big v8's in trucks hate short trips. Hammer is right, the truck isn't even getting out of closed loop operation, and is running pig rich all the way to and from your work.