Smoother joystick left hand side

I have replaced many joysticks and done the mods for the controllers. My son and his best friend play Madden with people all over the world. They are ranked in the top 2000 in the world. They keep asking for a smoother control on the joysticks.(Left hand side). I have tried different motors, lube,but they still trying too get it a little smoother.

Thanks if anybody has any ideas.