Just a SWAG, but try this:
Once you have your com port clearly established and the receiver connected (/rxn, /rx, or whatever)....
GPSDO-DB9 PIN2,PIN3,PIN5,PIN8 connect to PC-DB9 PIN2,PIN3,PIN5,PIN8
straight through - no crossing
Maybe try: 9600bps, 8 data bits, parity none, 1 stop bit, Flow control none
might not work but worth a quick try - key to try is straight through without crossing