There is one and only one fix. Ditch the panhard bar for a watts link. It is simple geometry, and Ford put it on other 8.8 equipped cars, but was too cheap to put one on the Mustang, citing it as a "luxury" item. I call it a safety/ performance item. Pamhard bars only work in theory, never in reality, since a bar cannot be of infinite length (slightly impractical for packaging).
2014 Mustang V6-Built to run TTB, CAM-C, and ESP
Proving to my fellow racers that the disdain that some GT drivers have for V6 drivers is unfounded, one results archive at a time since 2013.