Jumper the starter relay socket in the fusebox first - does the starter spin? Solenoid click?
No? - Jumper large lugs on the solenoid. Starter spin? No - bad starter. Yes? Jumper battery cable at the starter to solenoid wire - solenoid click? No? Bad solenoid. Yeah - bad wire to solenoid from fusebox.
Since you swapped all the computers that is the mostly scenario. Of course you can always have a wiring issue to the solenoid, but much less likey.

 

Well, we know the starter is good because the truck starts fine with the push button start and when in diagnostic mode of the security system with the scan tool.

 

Update, PROBLEM SOLVED!!

For those following or curious, the problem was indeed the XYZ switch.

When I mentioned testing it previously, I watched on a scan tool as I shifted through the gears and made sure that everything was being recognized, as well as the gear indicator on the cluster.

Anyway, I played around with the shifter and if I held it just right in Neutral, the truck would start with the key.

So I got the truck on the lift and behold, a BRAND NEW XYZ switch. Unfortunately, it looks to be of eBay quality and not branded and definitely not OEM. Got a good OEM XYZ switch off one of the parts truck, got it lined up now the truck is great. Key working as normal, no more ghetto push button on the dash.

Hopefully, my experience will help someone in the future from chasing their tail. Moral of the story, if no power is getting to the starter, start with the XYZ switch!