04 6.0 with straight exhaust and Power Service every tankt:

City 16-17 mpg's

Highway 17-20 mpgs

Towing 11k toy hauler 6.5-12 mpg's (to many variables to be consistent when towing ie. hills, headwinds etc....
The 6.5 was fully loaded with a stiff 35 mph headwind in South Dakota, I was only going 55-60 mph too! THat day I burned 1/2 of a tank of diesel in 150 miles, that was depressing!! I could only imagine what a V-10 would have done???)
To be totally honest though I had to throw in the 6.5 mpg, but that was only that one time which I'll never forget!! I usually get 9-11 on average......

 

I have a stock 04 PSD, and would like to raise mileage..

SO is the consensus that a "custom tunes" by SCT the way to go. I am also pulling an 11K trailer with it sometimes, but its my daily driver too. Running stock tires with a 3.73 at present. the mileage counter is saying 16.5 average per tank and almost 18 on a highway trip. Also what about intake/filter.. Looking for best bang for buck.

 

Sounds about like my mpg's! Mine is a daily driver and tow rig too. Have your muffler removed and it will spool faster and it increased my mpg's too. Do you run cetane boost in every tank? If not that will help too. Those 2 things are the cheapest mods for better mpg's, then I'd do an SCT...... Do not touch the stock airbox it is good for 500 HP. It filters the air very very good too!! That would be a waste of your money unless you are going for 500+ plus HP!