If it's only pushing coolant into the overflow after working hard all day, I'd start by checking for combustion gases in the cooling system before throwing more parts at it. A bad radiator cap, partially plugged radiator, weak water pump, or head gasket issue can all cause that symptom. Make sure the fan is operating properly and that the charge air cooler/radiator stack is completely clean, not just the outer fins. A cooling system pressure test and a block test would be my next steps.