Yes, go down in pitch on the prop 2 inches. That will get you another 400 or so RPM's and put you right where you want to be... This assumes that the engine has always run at the lower RPM's. If it ran better before, there are other problems that need to be addressed.. Let us know the history of the motor and more specific info..
If it helps you any, my Merucry '03 115hp 4 stroke came equipped with a Vengeance 48-16986 16P (16" pitch) prop. <br /><br />The engine is mounted on a 160 Dauntless Boston Whaler and turns about 5800 RPM @ WOT. Seems to be a good all around prop for my set up.
As Dave and Rick said, you need to lower the pitch.<br /><br />As a general rule, one inch of pitch is good for about 200 rpm-up or down.<br /><br />If you go down in pitch, you will notice that your acceleration will improve also.
