If you nuvi 3790 and your poi icons not showing when you send your poi via poi loader?
Then try this.
Go to the folder that contain your gpx file and bmp file
Make sure both have the same name
Right click on your bmp file, properties, Details, Bit depth (..)
If your icon bit depth is more than 8 bit then your icon will not appear .
To change it from 24 or any other size just do this.
Right click on the icon, open with, paint , save as, BMP picture, Save as type,256 color bitmap, then Save
Now recheck your file Bit depth it should be 8.
Connect your garmin, start poi loader clear the old poi and restart your poi loader and transfer your new poi and you should find the icons on you nav map.
Regards