2006 sx180 115 yamaha 4stroke.seems to run ok. but i only get about 5200 rpm.boat has a 19 pitch yamaha prop.and motor is in 3rd hole about 5 1/2 inches below pad.yamaha performance bullentin shows this set up turning 5800 rpm with a 21 pitch prop.is this something i should worry about?what should i do next? thanks for any help. ps i just bought boat and have only had it on the water once