As a test, see if Garmin Express will recognise a USB device (thumb drive or media card in a reader) as the dezl. Do this:
  • Format the USB device in FAT32 to ensure it's completely clean (Windows can be used for this)
  • Add a folder to it named Garmin
  • Copy the GarminDevice.xml file from the dezl's Garmin folder into the media's Garmin folder
  • Connect the media device to your PC then start GE to see if it recognises it as the actual dezl
  • If it does accept it, try to do the map download again - to the USB device.

If you added a basemap that's likely what is being shown with only major roads. You can check in the device's settings whether partial detail maps are actually onboard, or look in Windows explorer.