</font><font color="blue" class="small">( I might have been pushing too hard on the HST pedal (which paradoxically lowers power)...
I’m not sure I understand this, could you please explain a bit more? )</font>
An HST pedal is really a transmission pedal, not a throttle. If you push the pedal too far at once, not waiting for the tractor to start rolling, you're actually starting the tractor in it's highest gear range. Liken it to putting your 5 speed transmission in 5th gear and trying to take off.
With the exception of some of the new Masseys, the throttle is set to a certain RPM, and then one pushes the pedal evenly while accelerating and continuing to push the pedal further for higher speed. It will be instantly noticeable if you've overdone it, the engine will be trying to catch up. This is not particulary good for the engine and drive train.
Some of the new Masseys have HST pedals that actually act as a throttle as well or the hand throttle can be set. I haven't yet had the opportunity to try it out, but I like the idea of it.
John