recently my evinrude intruder has not been performing well at full throttle. It starts fine, runs fine, idles fine, jumps on pad etc. But my top end speed has been decreased by about 10 mph. No extra weight, same gas, same graph gauging the speed, same people in the boat. I always run ethanol treatment, and just put in some sea foam to see if it would help with no prevail. So in short, what could make my motor lack that much in performance at the top end?