Needing help diagnosing coolant overflow in 5th gen Cummins

[20215500RAM]

On a 5th gen RAM Dually 6.7 Cummins

Oooook, first off I would like to thank everyone who helped or commented/contributed to my last dilemma where my truck was in limp mode, it actually turns out my transmission was the issue….
ANYWAY, now I am having an issue where the coolant reservoir burps out coolant at high rpm when downshifting, it won’t do it in park at high rpm but only when driving, so here’s what’s been done
Coolant riser delete
Rebuilt 2018 motor with rebuilt flat tappet head
New Suncoast Transmission
New T-4 Smeding Turbo
Metal upper radiator tube conversion
New billet high flow water pump
New Mishimoto Radiator
New fan clutch and fan
Fleets rear of block coolant addition
New reservoir and cap
All new hoses
I’ll include some pictures here below shortly….

 

[20215500RAM]

Motor has less than 5,000 miles on it, transmission has less than 1,000 miles on it….

 

[Shaver Steve]

Motor has less than 5,000 miles on it, transmission has less than 1,000 miles on it….

Is there a slight black tint in the coolant reservoir, pushing coolant out is usually a sign of a bad head gasket on a turbo engine.

 

[Trash Panda]

I’m not sure what a “rebuilt flat tappet head” entails, but hopefully they checked the unit for cracks.

Last truck I drove that did this, ended up having multiple hairline cracks that ended up venting into the coolant passages in once the truck got hot enough.