I just wanted to make a post to share my experience. I have a 19 Laramie 4x4 with the 3.6. I bought it used. When i bought it i noticed the AVG mpg was terrible. ~15mpg. It was riding on stock tire set up which was 285/45r22 Goodyear Touring Eagles. I soon leveled the truck and had it aligned. ...I did some fuel cleaners and seafoam in the intake to help clean it out and was still gettign same mileage. My next step was to get the tires rebalanced.. I was told by two different shops that the tires were bad.. required too much weight to rebalance. i then decided to go for a more 'rebel' look and i ended up buying brand new Cooper ATP II in 275/70r18 with stock rebel rims. I was still getting terrible mileage. I re adjusted the tire size through jscan (jscan only gave an option to set as 33.1 or 33.25 for my nearest tire size) and my mileage was still down in the 15s.. on the Highway it was always hunting for gears. I took my tires back recently to Discount tires for a rebalance and rotation since i was going on a roadtrip and they said that my tires were off by 2oz on all tires. Pretty standard once tires wear in. So now my tires are rebalanced. I then decided to use AlfaOBD to enable the off road features in the head unit (I could never find the option on JScan). While i was in there i decided to go into Tire Aspect Ratio. AlfaOBD gives you more options for tire sizing. One of the options -- the one i chose was my tire size listed as "275/70r18 A/T". I set it as that and i have verified the speedo with an app and it is accurate. And now my MPGs have gone up considerably. I also noticed that on the same highway drive for my commute that i get a more efficient trip AND the truck stays in gear. also, hold 8th without hunting. Seems like the change to the actual size also changed the shift points. Overall i'm happy i saw more options under AlfaOBD. Just wanted to share incase someone could find this information useful later on. In all, if you dont have proper tire balance and tire ratio (which does affect shift points) set in the truck you could see a deminished MPG.
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