Zf 8 Speed P215C Code

We are having a problem with a 2012 Chrysler 300 with the ZF 8 speed. We changed the rear diff from a 2.62 to a 3.06 LSD and have made the correct gear ratio changes in the scanner tool (but I don't think the TCM is taking the gear change). The car is not happy, it keeps popping into limp mode under a semi-heavy load. In 6th gear, the car thinks it is going over 140mph. We are getting this code P215C, the transmission speed sensor is reading different from the wheel speed sensors which all of them have been replaced. I have reset all adaptive and re-learned the TCM. Also, reset the abs system, I am running out of things to try. Please any advice would help!!!