I am no guru by a long shot but have a couple of ideas. First on the depth issue I would check the software version to make sure it's up to date. HB has done some software updates recently to address the shallow water issue. If it is up to date then try switching the setting from freshwater to saltwater. With the GPS issue I would try hooking the puck directly into the unit just to prove that it does work. If it then works you at least know that the unit and puck are good and the problem lies somewhere in the interlink system. Then check your menu settings to make sure you have told it to see the puck. I know with ethernet the unit needs to be told which puck it should use, not sure if interlink is that way also. I'm going to let someone with more knowledge than me try to help you with your SI problem.