According to the SIMCOM Technical Support:
1) Command AT+CMUXSRVPORT is used to make physical UART interface for few virtual ports after AT+CMUX=1 enabled. And for host, there should be some special driver for linux/window OS.
2) Command AT+CGPSSWITCH is used to switch NMEA sentence output between USB –NMEA port (after install driver in windows, you can find Modem port, Diag port, NMEA port and AT port) and physical UART port.
So, if you don’t use CMUX, just connect physical UART interface, recommend AT command to inquiry GPS location, do not switch NMEA to UART. If you use USB interface of module, just get GPS NMEA output from USB-NMEA port by defatult. No need to switch.