Hello @obolland
according to the schematic GNSS_TX becomes M5-RXD which is then available (depending on set dip switch) on GPIOs: 3, 13, 16, 34 or 35 which translates to pins 13, 22, 15, 26 or 2 on the M5 Stack bus.
BTW: Since you are not stacking the module you can set all dip switches to 'on' at the same time (if you like).
Note: I do not have the M5Stack GPS Module v2.1 so I cannot test this myself.
Thanks
Felix
