I was out fishing the other day and was driving up river on plane. when all the sudden I lost power to my prop. I let of gas and and prop engaged again. after that happened every time i would try to throttle up my prop would disengage. the best way i can describe it is, just before the boat starts to plane in feels like a clutch slipping in a car, the motor revs up but seems like prop quit turning I let of gas prop starts turning again. It doesnt make any unussuall noise seems to stay in gear. this motor is in excellent shape and working order I am positve i didnt hit anything . Also it was very cold out that day and water temp was 40 degrees if that matters. any suggestion where to start to look would be appreciated.