I've got a JD 1760 12 row vacuum planter that I put surevac clutches controlled in 3 sections, groups of 4 and using a 20/20 monitor and row flow. The problems I'm having is when I plant point rows, as a section kicks off, the vacuum gets lower. When 2 out of the 3 kick off, the last section doesn't have enough vacuum to hardly plant. The  monitor indicated very low population and then I saw why. Any ideas? Also  when planting a square field one of the sections controlled by the row flow will come on later than the other two on a perfectly flat headland. Since they are all controlled the same, how is this happening?  VERY aggravating!!!