Slow vlans traffic with transparent to nat vdom

Hi all, Having some trouble with our current config (image attached). Basically traffic flowing from vdomB > vdomA will flow at full 1Gbs but traffic flowing from vdomA to vdomN is slowing to abound 500-700Mbps.  It doesn't seem to be an issue related to packets being shunted to CPU as that is sitting at 0% during any transfers.

Unit is a 501E so plenty of power. Any thoughts?