Just installed and ran your macro on my Nuvi 550... I've the following comments:
When I tried to use the POILoader you suggest (2.5.2) I got an error message. I continued the transfer and it seemed to work OK, but... I installed the latest POILoader (2.5.3) and I didn't get the error message and it seemed to load OK.
When I look at the Custom POIs I now have on the Nuvi, it seems to show about 52 and that's it. I went for a drive and it seems to show a different 52, I.E. it seems to be showing only the 52 nearest it's location.
When I went for the drive I didn't hear any alerts when I got near a cache, haven't looked into that too much but it seems strange.
I also haven't had a chance to check out the original reason I tried to use this macro... that being the limit to the amount of information the Nuvi will display for the Description section of the cache.
Thanks for the Macro,
Gord