Just tried this on my old nuvi 370.

The 4th & 5th map:
4) rename map4.img to gmapsup2.img and place in Garmin folder. Repeat the process to unlock the map, and name gmapsup2.unl

5) rename map5.img to gmapsupp.img and place in Garmin/App/ folder. Repeat the process to unlock the code, and name gmapsupp.unl and place in Garmin/App folder. This last map doesn't always work though.

does not work!
Anybody experienced success with Nuvi 350/370s?
If so, what firmware version?