Calibrate your speedo for the new tire size and she should start shifting as good as she did stock. Anything that can calibrate the speedo will work, the cheaper option will be Alphaobd but seems to be a little pita given the number of steps.
For example
I use Hptuners and with it is just one click, then it'll ask you for final drive gear ratio which (3.21 or 3.55 or 3.92 or any other gearing you may have) and new tire size (diameter in inches) and that's it.
Most tire size calibrators also work in similar way so adjusting tires/gearing is super easy with such options. Some may ask for tire diameter, others may have for circumference (Pi x Diameter) etc.
The secret is not to use the theoretical size of the tire, like a 35 is not a 35, in my case my tires are supposed to be 34.8" advertised, but if i measure the tire under the truck weight from ground to the tire shoulder edge, i get 33 1/4". In my case any of the 315's i've tried put my odometer spot on with 33.37", i'm a little **** when it comes to this stuff so i take my time with it.
![Smile :) :)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
Measure your tires from the ground to the should edge of the tire and use that number as yor base for the calculation then test your MPH against your GPS. you may need to adjust the number for the tire size more than once up or down, rinse and repeat until your odometer reads the same as your gps.
![50062561391_b92e0c3a0b_3k.jpg 50062561391_b92e0c3a0b_3k.jpg](https://www.ramforum.com/data/attachments/435/435062-85ee61c62335ffd1862fb7ec1e4d3008.jpg)
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