My buddy had an issue this weekend where his boat wouldn't go over 3000 rpm. I swear I just read a post somewhere saying someone else was having the same problem. Now I can't find that post. I tried using the search, but can't seem to find it.
My buddies boat is 2013 MB with the indmar. I can't remember where I read the post. He just got it back from an oil change. 3000 rpm max until after he shutdown and restarted. No further issues for the day. He asked me if I had ever heard of that, which I did, because I had just read the thread somewhere.
If it is idling long and then won't make RPM, you might have a temp problem. That would be my guess on a boat that new. Your temp gauge may not be working. Does the boat get louder???
I played with the GPS when it was happening to me, didn't fix it when I turned it off and on. As far as overheating, the gauge seemed to be working correctly, but obviously wasn't testing anything on the water that day. No overheating symptoms.