Open file GarminDevice.xml in Garmin folder with NotePad or any text editor. Search for text the gmap3d and the gmapdem. If you will found its you have no problem with SW and have problem with correct maps!
For downgrading to 4.80 you must simply copy the 4.80 firmware GCD file in device. !!! After restart you will see the warning about you will lose all your data as Favorites (your waypoints) and it is TRUE! Make backup for future restore before flashing!!! But If you have the positive result for my advice above you must find any mistakes in file integrity.
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