Bad EGR cooler?

[cantrucker]

truck is 2007 international 9200i with an cummins ISM engine 410hp with 300,000 miles on it.

I checked the CAC for leaks myself with some soapy water. Asked the mechanic to check for leaks in the EGR and perform a compression test on the entire engine & no leaks were found in either case. I checked the blowby myself seems to be minimal and an cylinder cutout test was performed and the engine ran even on one cylinder. I changed the IMAP & Delta-p sensor myself today and ran in the city and noticed some improvement. The truck now seems to pull better & black smoke is now is limited to acceleration and going uphill. Still get a warning engine at times on the dash above 40mph and coolant reaches 210F at times which seems to be too high to me. And a audible turbo whine can be heard when I let go of the accelerator.

The code that the mechanic told me yesterday was for excessive EGR cooler exhaust gas temps but I have bought my own scan tool online and will run the codes myself going forward. He also believes this is causing the engine to derate. But you are right I am beginning to pick up the wrench myself and learn and have unfortunately learned my lesson the hard way.