The problems is you have too many points on your map and to draw every point you have to connect to the google map API, which might not respond as quickly with that many points.
Pro Maps for Google includes a caching system which stores the map points in an xml file so you don't have to call the google map API each time which will result in more consistent results. However to use that caching system, you will need to use a dynamic page (PHP) with a record set.
Let me know If you need more information on how to create the map dynamically.