Agree with the fuel reduction. I use 50 percent and the 51 does fly better. Better, not like it should. Likely a CG problem. Most evident in pitch control even with the pitch slider full left. Results in excessive stall warnings.
My fix to 3 US P51d: Aircraft.cfg open in Notebook.
[flight_tuning]
pitch_stability = 1.5
Save and test flight it.
Make a copy of the cfg file if desired.