+1 for the motor fade, LRP X20s do that. Very doubtful it is the sensor lead, if it were you would have had some stuttering by now on acceleration from stationery.
Try another motor, gear the LRP down or take the timing down to see how much the fade goes away. Fade is not always related to the final temps of the motor. It gets too hot during the run, the performance fades and then the temps drop a bit so when you finish the run it seems OK.
Sort the gearing and timing out on this motor so it doesn't fade, or change to a more robust motor that takes the timing and gearing without fade. HTH
