You're most likely experiencing low boost during a regen, or erroneous temp sensor readings.
Low boost is often caused by the turbo. It doesn't really matter if the shaft is loose or tight, it just cannot ever bind. If it's spun by hand with a bit of side pressure on it and it binds, then it has to be replaced. Period.
The charge air cooler (intercooler, CAC) can sometimes get gummed up with enough goop to block airflow. If it looks like the inlet is full of tar, remove it and have it cleaned and pressure tested.
Sometimes the intake throttle valve sticks shut. It should be modified by drilling three holes in it. If it does not have holes drilled, get back to me.
If the EGR valve doesn't shut all the way, there can be regen problems. This issue is rare.
On the temp sensors:. The sensors should be replaced every 200k miles. Also, the wiring harness tends to break an inch or three behind the temp sensor connector because of vibration. This needs to be tested electrically. There is a TSB out on this that your dealer has access to. If they can't find it, get back to me.
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