Have set up the gps to load tracks onto sd card, and the file (gpx shows up there) but all tracks are not present.
First, realize that maps and tracks are completely different entities which exist separately from each other. Changing maps will not affect your tracks - they can be displayed on any map, or even without a map.
I hardly ever use my 60csx at all these days, so maybe they have changed the software? But AFAIK, you cannot "load tracks onto the sd card". There is an option to log your track to the SD card, but that file cannot be viewed on the GPS itself, it's only available for use after copying it to your computer.
With the 60csx, you must use Mapsource to send the tracks to the GPS itself. There is probably a limit to the number which can be shown at the same time. IIRC, you are only allowed a maximum of 10,000 track points.