Window sticker (I still have it, btw) was 13/17 for an '04 Hemi QC 4x4 and that's about right. Almost exactly what I got before I started modding it. But I think you're right 08Hemi1500, I believe they bumped highway mileage to 18 in '05 (why I dunno, save a couple PCM tweaks the truck was unchanged from '04 to '05).

I must have done some of the performance sh*t right, because right now I'm at 7000# which is a LOT over stock weight, running 35" tires and I'm averaging about 13/16.

As for the OP: Yeah you really need to use the search feature as this is asked/talked about daily. Of course when gas goes up, the "how do I get better gas mileage" posts go WAY up.

There is no magic bullet. There is no one thing you can do to dramatically change your MPGs with the exception of a tune up IF the truck is WAY overdue for one. New plugs, fresh SYNTHETIC fluids all around, cleaning (and grounding) the throttle body, cleaning the PCV and replacing the EGR valve will all help some.

Almost ALL modifications prove to cost more than they make up for in gasoline savings and would take an unrealistic amount of time (100,000 miles +) to break even. The ONLY possible exception to this would be to go to an EFAN which usually picks up a good 2 MPG in city/town driving conditions and cost is under $300 and can be under $100 if doing the "pick 'n pull" thing...

 

My average mileage since May of '10 has been 13.2. There is almost NO city mileage, just mostly 80 mph on the interstate. There has been some light trailer towing.

Any improvement provided by the add-ons you mention will take a long time to break even. Proper maintenance and a light foot is your best bet. That 9,300# trailer isn't doing the truck any good, either.