Brent, how much backlash?
IIRC there was about .0007" in both X and Y on my 325. I put new .125" balls in both (and it was a good opportunity to clean out the ball nut and all the chips lurking inside the knee/under the table) and the Y tightened up noticeably (about half as much) but the X is still about the same. That indicates to me that the X axis is the one that was getting the most use and had more wear.
Details the tips that I got and what I did to repack the screws.
I haven't checked to see if the bearings at the end of the screws are contributing to the backlash. It wouldn't surprise me if they might need some adjusting.
Anyway, depending on the amount of wear you have it appears that a lot can come from the balls, and they are dead cheap to replace. I'd give that a try first before you start spending big money, unless you are talking about a hi-time machine with .005" of slop.