Ray, thank you for the info. I'll look into it over the next few days. I rebuild engines for my Miata pals so I happen to have all that stuff, and then some.
For all those adding to this thread, check the backlash in a few places: the center of travel and the ends. I'll bet you'll find some differences.
So far I've lived with this by altering machining strategy to approach dimensions from the same direction on the ball screw, which has been very accurate.