I've got a Honda 2006 BF20D. I removed the lower unit last winter and replaced the water pump propeller. Boat ran good all summer until about mid way thru the summer the boat wouldn't pick up speed. The more you excellerate the engine the slower the boat will move. At an idle (trolling) it moves fine. If I raise the propeller out of the water and watch the revolution of the propeller, the faster the engine runs the slower the propeller rotates. In fact, at full throttle the propeller will hardly be turning. Can someone steer me in the right direction? What should I start looking for inside the lower unit? Thanks