When you state that you replaced the EGR, are you referring to the cooler? Usually when the cooler leaks, it will leak coolant into the EGR valve which will cause the valve to stick. When the valve sticks, you usually get a check engine light, but not always. It is recommended to changed the EGR valve along with the cooler.
What is seems that you are describing is that the EGR valve is stuck in a closed state and not allowing the gases to go through the cooler to cool the gases. Another concern is there could be air in your coolant sysem which could also cause this. The air would have gotten into the system from when the cooler was changed.
Some of those D12 engines have a small valve on the hard pipe that goes fromthe top of the radiator to the engine. Remove the cap from the radiator or reservoir. Open this valve. Start the truck and let it run. As it warms up for the termostat to open, air will bubble out of that small valve. Keep topping the radiator off with coolant as it lowers to halp push the air out of the system. This is "burping" the system. If there is no valve available, just slightly loosen the clamp at the top of the radiator and allow the air to escape that way.
Let the truck run for a few minutes with the radiator cap off at normal operating temperature so the air can all escape out and top off with coolant as needed. Shut the truck off and then top with coolant and close valve, put radiator cap back on, tighten clamp, etc. Run the truck on the road and see if that pipe still gets too hot. If you use a laser thermmeter and that pipe is reading at 220+ degrees, the egvavle is stuck closed and will need to be changed. My first choice would to verify that all the air is out of the system.
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