I agree with Alex's recommendation, check your connections. About the only thing that could be wrong with the motor is possibly bearings creating drag and/or the magnets getting weaker. If the bearings need replacing, they will be noisy and the prop hub will have some slight looseness. Also, the motor will be getting hot if the bearings need replacing. If the magnets are getting weaker they have to have gone thru some pretty hot running. IIRC, the temp has to exceed 180F to start causing damage, but I could be wrong on that.

I have many, many runs on my Himax motors and they run just as powerful as when new. A tach and amp meter are the real tools to measure this.

Kirk, a 20x13 is not much prop for the Himax 200. It is a fairly low kV motor so it needs a larger prop to generate the watts we typically look for in a 2M plane. Also, as the ambient temps increase a prop that feels fine at low temps can start feeling a little 'doggy' as the air thins. It's not dramatic, but you can feel it.

Don