I have only 3,500 miles on my truck, but I am wondering when my good mileage is supposed to kick in. The best I got was 18 when I had about 600 miles on it, but that was driving 40 MPH and skipping shifts so I dont think that counts. I was getting mid 15's doing 65 part way through Arizona when I was pulling a 20ft car hauler with my 6,000 lb truck on it, a 454 BBC and other stuff in the bed, but after I crossed into New Mexico my mileage went down, as low as 8MPG. Now, driving highway at 65-70 I am only seeing 16. When will it improve?

 

Generally mileage improves between 10-30K miles, depending on your towing. Do you have the 6.7L? Unfortunately, the 6.7 isn't comparing to the "old" 5.9. From what I've heard, your best bet is removing your emissions and adding a "black box" to appeal the ECM.

 

I have 11,000 miles on mine. I get 15-18 city/hwy (unloaded, hand calc). I don't expect it to get much better.

Last fill-up was $114.50, so now it sits most days while I drive my gas-sippin Honda...

 

I also have about 11,000 miles on mine. I get 15-16 MPG consistently.

 

Some parts of NM have winter fule and that alone will lower your fuel mileage 1-3 mpg. Also more hard working miles will help you get better mpg.