[Lowl!f3]

Make sure the thermostat isnt upside down. And your right about suspect head gaskets if evrything checks out unless hair line fractured head.. I have seen gaskets that block water ports or restricted them.
Also another simple thing to check is to see if your lower radiator hose is collapsing even if its new.

This may sound totally stupid but worth saying. Make sure the fan is pulling the right way and the water pump. Next is the right fan for the drive train. Dont know how much of a difference this makes. But when you go buy one at the auto parts they have different ones for the gearing. And fans with blades the other direction. Sounds dumb and can be overseen.

What size bag you put in those plated lowers? Looks like a 2500?
C notch???? No way bro. Thats a Step notch and a nice job making it!