Ublox GPS with Arduino Mega 2560 not working
The Arduino Mega 2560 has three additional hardware serial ports. Why not use one of them instead? Serial1 on pins 19 (RX) and 18 (TX).

void setup()
{
  Serial.begin(9600);
  Serial.println("uBlox Neo 6M Test");
  Serial1.begin(9600);
}

void loop() // run over and over
{
  if (Serial1.available())
     Serial.write(Serial1.read());
}


Cheers!