Hello,
I use GTN 750 for X-plane 9,11 and 12. But can only use XP Reality firmware version 6.62.4 as RXP hasn't updated the software for a long time. From what I understand, the RXP plugin must be adapted for later versions of GTN Trainer.
6.62.4 has a bug (Garmin) that gives the wrong course in the annunciator when departing on SID. This bug also had GTN in real aircraft. In 6.72 the bug is gone but cannot use that version because the RXP plugin is not updated for later Firmware (SW Version). However, GTN works with this bug. So in your case maybe you should stay with Trainer version 6.62.4 for RXP GTN. BR Stefan