Used to be in the old days, transmissions had interchangeable gear drives for adjusting the speedometer for different rears and tires. Is that the same today or is it done electronically? If I go to a 3.42 ring and pinion and/or higher tires does Dodge have a way to correct the speedo for this aftermarket r and p?

 

If you change the ring and pinion you don't have to make any changes. ABS sensors pick up tire (2 front and 1 rear on axle) rotation to calibrate speed so as long as you don't make a tire change (diameter) you don't need to change anything.