1989 Yamaha Pro50LF loss of power and running rough

1989 Yamaha 50HP long shaft.
Motor has run very strong for past 3 years.
Took it out the other day. Had a very hard time starting. Cranked on and off for probably 5 min trying to get it running.

Once it started and warmed up took off to our favorite fishing hole approx 2 minutes away. Motor ran fine. Lots of power as always.

Started up again fine. Took off and planned out, when motor began to loose power and sputter and run rough.
Lowered my RPM and it began to run fine again.
Again, up on plane, and within 10 seconds power was lost again. Back to idle and it ran fine.

Thought maybe it was missfiring, but as i removed each spark plug wire, the motor ran differently with each one, so i wasnt able to pinpoint which cylinder was the problem.

Here is a link to my youtube video of what its doing.

http://youtu.be/ojTMLisLPhs

any thoughts?

Thanks in advance

Could be a fuel issue and not electrical. As the RPMs increases, the motor requires more fuel. If there is a problem anywhere in the fuel delivery system, the motor may be starving for fuel at higher RPMs and be receiving enough at lower RPMs, hence smoother operation. Suggest you look to your fuel system, including filters, pumps, degraded lines, dirt, fuel contamination or leaks.

Model?
Compression?
Rebuild the fuel pump.
Clean the carbs?
While the carb is off check the reeds.
You using Ethanol in the fuel?
It can melt the inside of the fuel lines.