I have an 07' 6.7 CTD and am currently getting 15/16 mpg stock. What is out there to improve this that will not void my warranty. Tks Dan

 

You could switch to Rickson 19.5" wheels and G-rated tires. They should have less rolling resistance than your stock setup, and if you get a bigger diameter tire it will cut your RPM slightly.

 

From what I've read, your doing good at 15-16. How many miles on it? My 5.9 took a few miles before it started doing better then that. Have you towed with it yet? For the first 20K miles every time I towed my camper on the weekend, my mileage would get better the next week while driving empty.

 

Did you start the week with a full tank (that is, refuel after removing the camper)?

 

I burn at least a tank a week and log every tank in a database program that calcs the economy for me.

 

Try and Cold air intake and a bottle of power service grey bottle every month. Also try and keep the rpm's under 2k.