Have a 1975 johnson elect start, short shaft. Use it mostly for river fishing here in Texas. just started having this problem when I'm going up river full throttle the motor jumps out of gear into neutral, I can hold it in gear but know that's not good!! Took it to dealer they said no metal shavings in lower unit and they couldnt get it to jump out of gear. HAve it on a 14 ft flat bottom aluminum wide boat. Can anyone help?? 