First thing to assist with diagnosis, what is the fuel usage per hour, is there any coolant loss, oil consumption over a oil change interval? I have went round and round with several machines, a couple of them being exceptionally problematic with regen issues. Pre def 670 started out with not doing a regen. Went through every emissions test in service adviser numerous times, software updates, took several recording during regen attempts amongst numerous random codes. Finally done an ECU donate from another machine and a service regen was successful. Replaced the ECU and got the machine back in the field. That was a few years ago. I have replaced the ECU once since then for a separate issue. Also had an 660 with a frequent regen complaint that was not generating any codes. All tests in SA passed. Over the course of 3 or 4 years, All these same tests were performed including cylinder cut out test, electronic compression test, cylinder cut out test, etc. Finally this past harvest it was found through the electronic compression test, that there was a discrepancy between cylinders that hadn't been there before as well as a sudden increase in engine oil consumption. That machine was limped through to harvest end and subsequently traded. If the Tech can find a same level ECU to donate, that would tell you if the ECU is in fact faulty. If going that route, do not get a reman ECU. Only new. I have had too many issues with reman ECUs right out of the box. Good luck.