Brad's definitely right. Here is some code from the SoftwareSerial example sketch.
#include <SoftwareSerial.h>
SoftwareSerial mySerial(10, 11); // RX, TX
void setup()
{
...
// set the data rate for the SoftwareSerial port
mySerial.begin(4800);
mySerial.println("Hello, world?");
}
You should add (in your case) "ss.begin(nnnn)" with the appropriate baud rate for talking to the GPS.
Cheers
Ray