I have dealt with this type of skim key problem very recently. However mine was a ECM failure problem. What codes do you have? The ECM needs to have the VIN that is the same as the skim key. The flow as I remember it is the skim interface looks at the key, sends a start trigger to the ECM while confirming the numbers, then in your case the numbers don't match, it shuts off the truck.

What does Fleece say to do when doing this swap?

 

I can't look up any codes, because I don't have communication with the ecm. Which leads me to believe there is something vastly different with using a factory 5.9 harness and a 6.7/fleece conversion harness.

Which is super odd, because the 5.9 harness is incredibly simple, but there was indeed two connections I was not able to adapt into my 6.7 C2 harness. So I'm starting there, to use what worked before...6.7 C1 and C2 harness with the fleece conversion pieces.

Fleece doesn't give instructions, it's pretty simple. Their harness just goes in between the new ecm and existing 6.7 C1 and C2 harness.

I was trying to do away with the 6.7 C1 side of things mostly for aesthetic purposes, and it bit me in the butt.

Hopefully I can initiate comms again with the ecm and reflash it so I can get rid of all this skim/theft business and be on with my life haha.