Dear @audphile1 : I think you are in a " hurry " with a nec mc cartridge. Any cartridge needs at least 50 hours to sttle down many even more than that,
During those first 50 hours you need to run the cartridge at the high manufacturer vtf limit and could be better 60 hours.
After those 60 hours you must re-set the overall cartridge/tonearm alingment and cartridge set up parameters and that's it.
Be patience.
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.