You would be better off using SERIN2.
Here is a snippet from something .
Code:
SERIN2 PORTB.2,16572,[WAIT("$GPGGA"),WAIT(","),DEC2 H,DEC2 M,DEC2 S,_
        WAIT(","),DEC2 ND,DEC2 NM,WAIT("."),DEC3 NMD,WAIT(",N,"),_
        DEC3 WD,DEC2 WM,WAIT("."),DEC3 WMD]