Just wanted to update this thread:
Truck is still at the dealer. I was transferred over to the GM helpline and was initially denied claim in full at just over 3k miles out of warranty. A senior advisor closed the case without even calling me which baffled even the dealer.
I called them back, reopened the case and sent a letter to the GM CEO and upper Execs of GM. Believe it or not, CEO's assistant contacted me the next day after reading my letter about these faulty CP4's. They are doing an investigation on them and moved my case into the department that investigates recalls and major safety violation issues (I lost all power to my truck, steering brakes, etc. -- glad I wasn't pulling my 20k pound trailer at highway speeds).
Right now GM has requested fuel samples and that is being tested. While I definitely do feel like GM is doing all they can to find some way to deny the overall major problem of the CP4 and my claim, I still appreciate the length they are going to and how quickly they escalated things. We will see what they say considering I always go to busy diesel stations and major brands like shell.