I have a 1972 Mercury 9.8 HP that runs fine from idle up to about 3/4 throttle. When I open it on up to full throttle, it seems to jump out of gear. The engine is still wide open when this happens. I throttle back down to an idle speed and the boat will start moving again. I don't hear any bad noises when this happens. I first thought I had a spun hub but this is not the case. I replaced the whole prop but this still happens. I marked the hub to make sure it wasn't slipping too. The only time I move the gear shift lever is when I first put the boat in the water. When the boat stops moving forward I simply let off the gas and it will start moving again. Thanks for any help you can give me!