We do a lot of molds using tabs and slots - but we've recently noticed that the further from 0,0 we get - in both the X and Y axis, the more variation we're getting in the width and length of a slot/tab. It seems to be a linear relationship, getting worse the further from home we get - being off by as much as .040" over the full 96".

How do we correct this?

We have been using our Shopbots for over 15 years, and have been letting it slide, because it didn't matter that much - but now we have projects that we need it to hold tolerance anywhere on the table.
Thanks for any help you can offer.