I have a 2008 Blazer 202. It came with a Yamaha 200HPDI; I recently replaced the 200 with a 250 HPDI. Engine setup is as follows: Mounted on the 2nd hole using a Slidemaster Jack Plate. Jack plate is set to 1 5/8 inches high, currently turning 56 - 5700 RPM ; 71.5 MPH (GPS) Using a Yamaha 27 M Prop. I feel that I should be in the high 70's. Any suggestions?