Intermitent Derate alarm

[BDiscovery]

2014 Cummins ISX 15.

Engine was replaced at 450k, truck now has 560k. About 8k ago I pulled off the dpf and doc and had them cooked/cleaned. All new sensors on the dpf filter, temp and pressure. Also just replaced the def filter. I also pressure tested the coolant system for 24 hours and almost 0 pressure loss. I was try to see if the egr cooler was leaking.

I'm getting intermitent derate in 2 hours, then check engine, then goes off. Then back on derate in 3 hours, check engine then off again. This started after the def filter was changed, not sure if that had anything to do with it or not.

Also getting dpf overheat alarms.

The driver just had speedco put a computer on it and was told there is a code for the egr cooler and a code for the turbo.

Looking for help.

Thanks,

Brian