I may have caused confusion, I have the "06" in question and a "00" 1ton dually. Both have KM2 tires, both have less than stellar mileage figures. I left out the specifics but its a stock truck other than the tires that are specked out at 34.3" but really about 33 1/4" installed on stock rims. I did not re calibrate or chip, etc.
I have 3.73 gears with an auto and it is fine other than towing through CA, I get poor mileage. The issue is it is to much rpm in 3rd while towing and to low of rpm in O.D.
I did run into a very detailed discussion of yours after I posted this, causing more thought about size and width and rolling resistance along with rpm facts from cummins, but I still need to decide on:
#1 swap to smaller tires -side note about mudders vs all terrain and rolling resistance
#2 install a chip hoping to move the torque curve and shift points to accommodate the change or
#3 live with it. Gear change or "gear vendor" is a lot of effort for some looks .
Will a programmer get me by or do I need to go back to stock until I can change gears or get a gear vendor?
I would like to keep the big tires and get by with a programmer to fix the issues above. I like the lower rpm with the bigger tires but I can see that its an issue.