2015 merc 30hp low power and in limp mode

[dieseltech97]

I have a 2015 mercury 30hp efi engine that I bought new and it ran great until last year it randomly would lose power while cruising at wide open throttle and now its to the point where I can only run wot for 5 or 10 minutes before the alarm goes off and it goes into limp mode. Some times it will do it every time I go WOT other times when I'm out fishing it wont do it at all. I brought it to the dealership 4 times and every time they say nothing is wrong and they can not get it to act up. The last time it was in they inspected the water pump and said its good but of course its still doing it and is now out of warranty. When the alarm goes off it keeps going until I shut the engine off way 10 seconds then re start it then I am good to go and a lot of times it will not do it again until after it sits for a half our or so. The stream is good, never feels hot just warm, I am wondering if it can be the temp sensor telling the ecm the wrong temperature and if so does anyone know where it is located? I have though about it being an over rev alarm but it doesn't go away when I idle down only when I shut it off and the prop is still the factory prop that I used and never had this issue for the first couple years. Any help would be great I am getting so frustrated with this motor!