I'm at 1 every 3500 right now, which is basically every 3rd day or so. I just want to complete a week without a mis-sort, I'll feel way better about my situation. This week is already a scratch cuz i had one yesterday, bleh
Mileage varies from center to center, obviously; that being said, I'll make a remark or two relative to the operation I work in.
I'm not sure when this happened, but just showing up to work every day, caring about what you do, and trying your best is now the mark of an exceptional employee/person. My philosophical feelings on this phenomenon aside, the reality is that if you do those three things (as someone else intimated), it goes a long, long way in the building where I am employed.
That is not to say you should not continually analyze what you perceive to be as your shortcomings and try to improve them, but it sounds like you have some ground to stand on already. When you take your average kid off the street, and throw them in the cauldron that UPS can be, most quickly give up because "it's not possible", or quit. So, consider it from this perspective - if that is not you, and you still try hard on the really, really bad days, then management would be stupid to let you go.
For some additional context, there have been 6 seasonal hires in the building where I am employed (sequentially, not aggregate) - every one washed out, quit, or was told to stop coming to work because of extreme performance shortcomings; we just lost number six on Monday.
All that being said, there are no guarantees in life; so, good luck.