Thanks a ton for sticking with this. It was a combination of the CUSTom and that I was running older FW. Upgraded to 1.37R10 and now I'm seeing exactly what you're seeing. That's what I needed!
>>>:FORMat:DATA?
FORM:DATA CUSTOM,7
>>>C1:PAVA? FREQ
C1:PAVA FREQ,3.003000E+04Hz
>>>FORM:DATA CUSTom,6
>>>:FORMat:DATA?
FORM:DATA CUSTOM,6
>>>C1:PAVA? FREQ
C1:PAVA FREQ,3.00300E+04Hz
Simon