Not an expert Lee but on my tc55da my curl down is slow. I think it's in the joystick control. I move it around and then it will start working better. Dad's NH 2120 was finicky too.
Good ideas guys. I'm not familiar with the particulars of NH machines. When either of your machines are acting up does it load up the hydraulics like Lee said his does?It could be that your curl cable needs a slight adjustment.