I have repowered my 18' 89 Ranger 363V Bass Boat with a 2118 F150 Yamaha O/B, engine came with a 14.8X17 Aluminum Prop. I want to go to a SS prop and need advise on correct pitch. Currently I get a great hole shot but only getting top speed of 45mph at 5800 rpm, any higher rpm loses speed. Old...