80 HP Yamaha 4-stroke won't maintain highest RPM

[lbscoob20]

Got an issue with a 80-HP Yamaha 4-stroke on a 17' center console.....when accelerating the engine sounds fine and at full throttle gets up to ~5500 rpm sounding great. About the time the boat planes off and is "steady" the engine RPM's drop down to 4400-4500 and stays there consistenty. At 4500 RPM the motor still sounds great....no obvious signs of missing or anything strange like that. It just won't keep up with the 5500 RPM range that is typical.

Thanks for any thoughts.

Scott