I am very close to returning the Humminbird 597 ci hd di. I have been having allot of problems with it not reading the correct depth...it flashes back and fourth to correct depth, 0 to 2 ft, 1000ft etc...the sonar graph is a total mess also... especially when beyond 150 ft. The salt water setting is on deep. Now I cannot get any GPS speed, maps or waypoints at all. Does the GPS speed have to be programmed in or should it come on automatically... Thanks, Andy