Clear the non-volatile memory:
Speedometer -> Developer Info -> Non-volatile -> Clear non-volatile.
Clear non-volatile memory probably is more complete than Master reset
Garmin's Nuvi's do not have a hard drive. Everything is stored in memory.
NVM or non-volatile memory,it is Nuvi memory that can retain some stored information even when not powered. Some files, like the Operating System files, are stored in non-volatile memory and others like POI files are stored in volatile memory that is kept alive by the battery.
Removing the battery will completely erase everything in volatile memory-
Clearing Non Vol erases all the files added from your usage since you powered it the first time.