Hi all I purchased a 1999 Key largo 160cc and it has a 99 Johnson 70 hp on it the prop that's on it is a 13 3/4x15 the rpms at wot are 6000 and the boat is only going 28mph. I have a prop that my prop guy made me witch is a 13 1/4x17 and it's no better. The boat is not a heavy boat and it's...