CM870 ghost derate

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This is my first time on here, so I hope I don’t screw up too bad. I have a 2005 Pete 378 with a 475 ISX CM870. I’ve been fighting this truck for a long time and I’m at an impass. Truck loses power not long after taking off. It is derating although there is no CEL. I can pull over and restart the truck and she runs great with good power for a mile or so and then same thing, it just loses power like a derate. I’ve heard of a “ghost” derate but don’t know where to start. I just bought this truck and have no history, but someone has been fighting it before me. I’ve found and repaired numerous issues, but can’t get to the source of what it’s doing now. Nearly every setting in the ECM had been messed with and was wrong. I’ve even sent the ECM out to be repaired and they said it’s good. Is there anyone here willing to point me in the right direction, I’ve not seen this before.