I may not be 100 percent sure that my prop isn't opening all the way - it is pretty hard to look under the boat to see if it is, but I can't believe it is a problem with the reversing gear because when my prop finally does open all the way it drives the boat just fine and has plenty of thrust. And there is a lot of vibration - like something is really out of balance when it doesn't open corectly. I cannot see how a problem with the reversing gear or transmision could be intermitent. I have to believe it is the prop. Sure the centripital force wants to open the prop but the water flowing past the prop wants to close it.