Need help with a StreetPilot c550... (zoom out problems after 2012.3 udpate)

Street Pilot c550 was working fine until 2012.3 map update. Now, when I zoom out on map (or to view a route) to 120 miles, unit takes almost 2 minutes to load map and some random states will be blank or partially blank. If I zoom out to 200, 300 or 500 miles the screen goes blank and doesn’t even say “loading map”. When zoomed inside of 120 miles the map works fine and I can scroll around to all regions of the full North American map. Garmin C.S. unable to help. I have tried reloading the 2012.3 map update with both the lifetime updater and map updater programs a couple of times now to no avail. I would like to manually delete all map files from the unit and try to install 2012.3 from scratch. Which files would I need to delete? Any other ideas? Few other things I have already tried were: 1) deleted all favorites and poi’s. 2) tried both methods of resetting the unit. 3) looked for updates on WebUpdater and myDashboard (none available, already up to date). 4) already have a newer unit (nuvi 2595 in the other car). Any help appreciated.