Everything that you describe is much the same as I have done with my Nuvi 205W (I haven't done much about routes up to now) except I can see the OSM mapping.
I've never bothered to try routes in there but I can see the tracks.
Occasionally, the Nuvi doesn't "load maps" OK with the SD card inserted (sometimes it does, sometimes it doesn't); then I switch it off, remove the SD card, switch back on to load maps and then reinsert the card in it's slot; after that the Nuvi can see the OSM map.
I suggest you experiment a bit, on these lines (or re-download the OSM).
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Dave
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