Are you saying that you've boiled the 325 gallons down to 10 gallons of concentrate?

Syrup is just sugar and water and if you've boiled off the excess water, the sugar should be in what's left. I don't think that drawing off too early can effect that. Are you pre-wetting the filters? You could be losing some syrup there.

I know that the sugar content has been reported to be low this year (seemed about average to me) but I wonder if either the sugar content was extremely low or you actually had less sap than you thought.