From the discussion, it sounds like 0.6*5V = 3V input to the Arduino should be
ok, but if you chose to do level-shifting, then rather than wiring up a complete
chip, you could use
-
a series-diode [1N914] and pullup resistor [4.7K to 5V] on the TX out of the
GPS module, to give 3.3+0.7V = 4V input to the Arduino. -
a simple voltage divider[as others suggested], 2.4K series w/4.7K to ground
on the RX input pin to the GPS module.