It’s unfortunate the air turbine wasn’t being used for the testing.
It’s a great tool for helping to find valvetrain stability issues.
My experience has been, that when the power makes a fairly sudden drop...... like in one line...... it’s often a valvetrain stability problem.
When in doubt...... try and go a few rpm higher....... especially when the top of the run is at a pretty modest rpm anyway.
I’d like to see the fuel flow numbers myself......... the bsfc numbers are fairly poor(how efficiently the motor is using the fuel).