Seems funny this has gone unanswered for a year but if you are still in need of an answer the numbers you listed are Northings and Easting from the UTM (Universal Transverse Mercator) they differ from lat/long in that they are metric distances referencing a zone based system that is commonly used on land maps, having parallel vertical lines instead of longitude. They always go east then north based on an X/Y system as apposed to lat North or South then long east or west there are no negatives.
The number is in metres from the zone datum or boundary, there are 60 zones (longitudinaly 6deg apart) starting at Long 180.
Your GPS should have "units" for coordinates of DD.ddddd, DD MM.mmm, DD MM'SEC' or UTM. Just go into the units setting on your GPS and change lat/long to UTM and all will be revealed. Complex to explain but simple to use.
Be sure to set the datum, if it is a new reference it is sure to be WSG84.
Kevin H