Lots of things to mess you up reloading your own ballnuts.
Any noise on a ballscrew is bad.
I'm a bit confused on the ball sizes used. Where did you get them?
Preloaded nuts generally use 2 different size balls. Every other ball is slightly smaller. The second ball acts as a spacer and "floats" in the ball channel so that the balls aren't fighting against each other. You don't measure these kinds of balls with calipers.
Also of course everything must be super clean. Nuts, screws, and balls are usally cleaned in an ultrasonic before assembly.
I agree that high rapids are very desirable. I find anything that can't do 10000 mm/min like watching paint dry, but I'm spoiled as my CNCs run at 20000 mm/min.
Bob
You can always spot the pioneers -- They're the ones with the arrows in their backs.