Those symptoms don't ring any bells for me, but I don't know a lot about the diesel engines.
I would start by getting hold of a code reader (a.k.a. scantool) and plugging it into the computer's diagnostic port, and seeing if it's storing any codes - it could point you (and us) in the right direction.
You could go to a dealership or mechanic to have the codes read, but TBH it's probably easier to just get a scantool from eBay.
Something like this.