2007 Yukon Denali won't turn over

[Jetlag]

Opened the door and running boards didn't come down. Turned the key to start and nothing not a click not a thing. I hear the fuel pump pressurizing the radio works. With the key in the run position I have no gauge information needles don't move all are dead. No information at the OBD2 port. Going from off to run all system test seem normal. Battery fully charged, mega fuse checked all fuses underhood and left side of dash checked ok. Shook battery cables tried to start in neutral still nothing. I'm leaning toward the ECM with the no gauges and no start. Also I believe that the running boards will not extend if the vehicle is moving. Drove fine one hour before. Luckily it died in the garage. Anybody have any idea of what to try next. If it is theECM can it be removed and taken to the dealership to be re-flashed. Hate to also have a big towing bill. Thanks for any reply.

[GLSierra13]

Could it be the ignition switch or the passkey (passlock?) security system? We've had two GM cars act similarly and both times it was the security system related to ignition switch failures.