Bass - That Johnson 225 is a mean motor. How do you have it setup? You should be able to bump it up a few holes . . . What prop are you running? If you can find a nice 17P Viper . . . I'll bet you'd be a happy man.
Here's performance specs from a 2.6L OMC seadrive . . . those were about 205hp at the prop from what I understand but they had the heavy bracket / trim and tilt.
http://www.classicseacraft.com/broch...Drivefront.pdf