I've got a 2015 2075 GL Tri-toon with a 150 HP Yamaha. Bought it new at the end of the season in 2015. (about 85 hours on it). Boat has never gone faster than 30 MPH. (5400 RPM). If I trim all the way up I can get 6500 RPMS but no increase in speed. Original prop was changed after complaining to dealer ("wrong prop"). Currently running a Yamaha Reliance 3 blade 15-M, 14 1/2. Anyone have any ideas? I was originally told boat would do 40 MPH.