Did your nuvi behave differently before trying GarminCure3? To check it, try flashing ORIGINAL firmware.
Now I know that your firmware is really started by the bootloader, because there was an infinite loop at the beginning of the firmware in the second RGN.
Now I want to find the exact instructions of the firmware that cause crash/reboot. This is a very long process, so let's do it in private, and then just publish the results here.