I am currently having issues with my 2005 Mercury 90 hp Optimax. The motor is losing power when under load. Had it out yesterday and the first time I drove it, had no problems. About thirty minutes later, it would not go past 3500 RPMs and would only go about 7 mph. I had this same problem a few weeks ago and I could turn the motor off and restart it and it would run with no problem. This has become an intermittent problem. I recently changed out the plugs and wires after the problem first surfaced. I again turned off the motor and restarted it, but still no success. When the motor begins running like this, the motor seems to have a lot more vibration to it. Anyone have any idea what I should check for?