I would be VERY impressed with THAT kind of miledge with THAT kind of load, especially in the winter months...!!!!
Do the air cleaner kit, and a magnaflow muffler, the mpg`s will get even better.
Get rid of the resonator`s on the tail too... let it breathe...!
Just becareful in town, it`ll bark at the POlease an then you`ll get a ticket.
I have a 2010 Hemi RT truck, best i`ve seen yet is 15mpg with it...
BUT thats easily explained, my right foot is usually stickin thru that pretty grill