This may be an issue with a "locked" LB7 ECM. I have bricked a few of these over the years during reflash. The previous flash will take (sometimes), but EFILive or the dealer Tech II cannot get in an unlock the ECM to do the next flash.
LB7's are notorious for this, so any more, I remove the ECM and do a bench flash with one of these:
https://bench-force.com/collections.../benchforce-starter-kit-for-automotive-obd-ii and associated other required harnesses. You can also make one yourself for a LOT less, but I had no time and was in a hurry.
It is not absolutely necessary, but I was tired of bricking the ECM while doing the flash in the truck and then sending them to SoCal diesel to have it fixed.