Sorry if this is in the wrong forum but I wasn't sure where else to post.

We have a 2005 300C that we are in the process of installing a 3.91 Getrag center section in with new axles and hubs. What kind of tuning problems am I going to run into once this is on the road and do any of the box tuners have the capabilities to make the needed changes for the ECU and trans controller to work correctly with this change?

Thanks!

I don't think you'll need to make any changes necessarily. A tunes always great to make the best of it. I know on the trucks they get their speed input from a tone ring on the ring gear so it doesn't matter what gear you install, the speedo will still be correct, but I think the cars get it from the output on the trans? If so you'd need a tune to get the speedo working correctly. Now that I think about it, if the speedo is off and the rear wheels don't match the front through the ABS sensors it might give you problems. The Mopar 11 Chargers had that combo factory (5.7/NAG1/3.91's) btw

No cars, and trucks with 4 wheel ABS or ESP get vehicle speed from the 4 tone wheels through the ABS/ESP module. You will not notice a difference on the speedometer unless you change tire rolling diameter. The only thing that may happen is the computer realizes your turning more RPM than it would like to see for a given speed and think there is a problem inside the trans. But I believe the 580 has input and output shaft speed sensors that would prevent this from being an issue.