HELP PLEASE!

[Colorado Bass Man]

I have got a 18 foot 1989 astro bass boat with a 150 mercury on it. It does about 45-50 MPH and I would like it to do about 60. I have the right prop but were only pulling about 4000 RPM, the factory spec's say max would be 5500. How could I get to 5200 or even 5300?

What can i do do make it faster? 

[BassBUFF]

Sounds like the motor is not running right to only get to 4000. Are you sure it's hitting on all cylinders? When was the last time the plugs were changed?