3458A opt 002 AC Synchronous Flatness Issues

[gb3]

I'm having issues with the flatness of the Synchronous AC on a 3458A that I'm calibrating.  The 1V range at about 1Khz has a sharp rise in value, and it reads out of tolerance at that point, but all the other frequencies on that range are good.  I looked into the adjustment procedure, and found an AC flatness adjustment, and performed it, but it only adjusted the high frequency flatness and gain; The low frequancies were still not flat.  Is there a low frequency adjustment for this?