Nag1 Limp Mode After Rear Gear Change

I recently installed a Getrag 3.91 differential in place of the OEM 2.82 differential. Using the HP TUNERS, I'm not able to write the new gear ratio and tire size. I'm getting, "failure to write" message. I drove my car around the block and noticed that it's not shifting, not even with autostick. Autostick is not working and it just reads D on the cluster. Limp Mode.
1.How to write the new gear ratio? (Clicking the green power button and following the prompt gives me a failure to write message)
2. How to clear Limp Mode?

1. Have you purchased credits to be able to write?
2. Click on the diagnostics and info button in the VCM Scanner and then click the button to have it read if there are any DTCs and then clear them there

I have credits. I will see what codes I have and clear them. Perhaps that's why I'm not able to write the new gear ratio. Thank you.

I reset the TCM. However I'm still not able to write new gear ratio which throws my car back in Limp Mode. I'm getting failure to write new settings.

Nevermind. Somehow it just wrote the new gear ratio. I cleared the TCM about 30 minutes ago and it now accepted the new write. Thanks you.

Did you get it fixed? I have been having the same problem on my 2008 Challenger and HPTuners Scanner said it updated but the car would go to limp mode. The only fix was to update the tires size and gear ration with my Diablo T1000

Yes I have got it to work. I had to clear the TCM DTC, initialize it and cycle the key. I had to play around with it to get it to work. I don't remember if the key was in the on position or cycled off because I I tried both. Play around with it after you reset the tcm.