Jay, I wouldn’t be surprised if the header flange nuts are loosening under hard load(alot of heat). Have the guys @ Synapse drill a set of 6 nuts for you and safety wire them after installation(torque then wire). If all the appropriate turbo support brackets and rear DP to transmission bracket are solid, the exhaust moving around back will likely have little to do with it.
I’m not sure of your exact setup but FWIW info wise, stainless header flanges expand quite a bit under alot of heat, which can stretch the fasteners and then as the flanges cool after a run the vibration of the motor can rattle the bolts loose. Just a little at a time, but enough over multiple heat cycles until the tension on the gasket is low enough that it blows. If you’re constantly blowing gaskets out, it’s worth the money spent to have that done on top of anything else you may have them do while they’re under the car. Or have them install some steel lock tabs under the nuts(common race part that can be purchased all over the place or made to suit)
Car sounds like it’s running good now!