Direct connection between GPS and Uno produced data garbage. 1Hz unit is normally at 4800 baud and the 5Hz unit is defaulted to 19200 baud. The output from Garmin is inverted. To correct it feed the input from Garmin to the base of a 2N2222 thru a 10k resistor, connect the emitter to ground and the 5V out from Uno to the collector thru a 10k resistor. Now take the output to the Uno input from the collector of the 2N2222. Make sure you tap the output from between the resistor feeding the collector 5V and the collector pin. This simple inverter fixes the garbage you see on serial monitor and you will see regular NMEA data. Try out the TinyGPS and TinyGPSplus libraries, they are very helpful for parsing the data.