Check the High Current AC wiring check the wiring is properly sized for the current and ensure all crimps and connections are secure.

Version 3.7.8 of the firmware was the initial release of the Temperature Monitoring and throttling safety feature. The thresholds for temperature throttling were set to very conservative values (starting at 52C). The latest firmware version 3.9.6 and greater increases the temperature thresholds by 10C. 

Example of a 40A charge with threshold set to 62C.