I'm running totally full throttle, balls out, but moving less than walking speed. In no way am I trying to run lower RPM, that's just what I get because of the load on it.
The only other thing that I can think of is the fact that I'm set very low, 1 x 1" spacer on the bottom of the front wheel yokes and 2 x 1" spacers on the bottom of the rear wheel yokes.
Possibly, being that it's set so low and tight to the ground... Maybe it's struggling to suck air and doing a lot of work to fight that drag in the airflow? I'm going to try 2 x 1" on each front yoke and 3 x 1" spacer on each rear yoke and see if that has an effect on it.
After that, the only things left would be drag on the spindles turning the blades, or drag in that gear box. The blade spindles all feel similar, so unless all 3 are degraded the same amount, I'm saying that the spindles are fine. The gear box, I'm not sure how to know what is normal drag and what would be excessive. I'll try at least one more time though when the grass is ready to cut again.