All the NC7 code does is basically default the emission system configuration to the more stringent system, like what is installed in Ca, NJ, Maine, etc. So if your vehicle has the California emissions RPO code, YF5, it is exempt from the federal emissions, since it is Ca. compliant, which is more restrictive. Merely a 'book keeping' thing:
http://www.gmfleet.com/content/dam/gmfleet/global/master/nscwebsite/en/Home/Resources/01_images/2015-model-emissions-bulletin.pdf
While the tune may be different between the federal and Ca., etc., tunes, ALL of them, from GM, will still have AFM activated. Most Departments will keep this tune, since a retune by the Department motor pool will void warranties, especially if the AFM lifters fail, and the AFM has been disabled. That's an expensive fix that NO Department wants to pay for.
If AFM is disabled on your truck, either the Department did it after the truck ran out of warranty (unlikely, as that's just extra hours spent working on a vehicle that's really not necessary, especially since that vehicle may soon be retired), or, more likely, there was some party that took possession of this truck after the Department was done with it and tuned the AFM out.