ADSIBNR171

I just re-geared my 2015 2500 from stock 3.42 to 3.73. The difference is noticeable, but not significant. The place that installed them said I had to take my truck to a dealer to have the ECM flashed and updated to accommodate the new gears. That made no sense to me as the gears are obviously mechanical not electronic or electrical. So I made it to 3 dealers. 2 stated that they had no idea *** I was talking about. The third said it would cost approximately $135 to flash the ECM, but was unable to confirm that it would change settings for the new gears.
Does anyone have an idea?

1-2-3

They probably mean that you need to update the speedo settings for the new gears. I the old day, you changed the speedo gear in the tail of the transmission. They had different color spoeedo gears to go with different ratios. Now it's a ECM setting.

BarryG

It is as 123 said to reprogram the ecm for the speedo. You should be off about 9% with that gear change. I think it could also affect the shift points if an auto trans. A simple reflash/update isn't going to change it they need to go in and change the parameter.