No crank no start?

Okay, but the Low-speed network having no voltage at all, can be the no start issue, we've just been through so much information on the BCM, we need to get a voltage on the Low-speed wires. It should be around 7volts. Just check Pin1 of the DLC and the two grounds 4 and 5.
When you mentioned that BCM X2 pin 22 was grounded, do you mean you had zero Ohms on that pin with the BCM unplugged?

Here is the 2nd Splice location for the Low-Speed network. Under the passenger seat with all dark green wires.

Take look at this video, it explains the GMLAN low speed network operations and what might be going on with your vehicle, having no voltage might mean that it's shorted to ground.

https://www.youtube.com/watch?v=Rwsfe4KT330

So, connector X2 pin 22 unplugged showed 12volts? Or is that coming out of the BCM pin?
X3 pin 10 should not be grounded, that's the problem with the Low-Speed network, there should be activity on that wire for all the other modules on the Low Speed.
This JX 339 is the other Splice comb that needs to be checked, there might be a module or short to ground pulling the network down completely.

The X2 pin22 is an Accessory voltage that should be coming out of the BCM.
With the BCM unplugged, can you communicate or pull codes from any other modules?
Try communicating with the EBCM(Electronic Brake Control Module).

Okay, you need to find the other Low Speed network splice comb under the passenger seat and unplug it and check to see if any low-speed activity comes back. I posted this case on the All-Data community as well to get some other techs thoughts on this. I'm concerned about that Low-speed network being completely down, I'm wondering if that being shorted out will pull down the BCM, because your scan tool is not showing any modules on the low speed at all. And it should be scanning every module in the vehicle. The BCM is the only module that is on both High and Low speed GMLAN. Hence the need to pull the other splice and check for anything coming back online.

Sorry about that, I'm just now seeing your message, the other splice pack should be under the passenger seat, yes, it should have all dark green wires just like the other one, the wires might be a little darker than the other splice pack but still green. So, it seems like the BCM is still putting out the Enable and Wakeup voltages it should be, but you can't communicate with it. I just want to be sure that this is not being caused by another module on the Low-speed network pulling down the BCM. That could happen, I'm also going to check on All Data to see if I got any responses about the Low-speed network wake up signal. But when you find the comb under the passenger seat, make sure that it is the only connector you unplugged. Once you have the connector unplugged you should be able to see the comb inside that is splicing all the network wires together. The comb should still be inside the network splice pack. I don't believe they come out by just unplugging the outside connector, you might need a pair of needle noise pliers to get it out. Then check each pin for any voltage. Make sure the BCM is plugged back in first. Then turn the key On and check it. If voltage comes back, Leave that splice pack unplugged for a minute and check that voltage returned on the other one.
The JX 339 is a black 12 pin end connector.

Still only 0.3 to 0.5volts? This is a difficult case. Without being able to scope the network and see if the High-Speed Bus+ or Bus- is showing something off, it's really tough making a call here.
Are you able to access any of the modules besides reading codes? Can you go into the ECM or TCM and read live data? Or access the BCM or any other modules?
If we follow this Circuit testing flow chart, the no comms with the BCM unplugged points to a failed module, but I would expect Low Speed network activity, unless the BCM is responsible for a Wakeup signal to the Low Speed network, and I can't find any information stating that.

Those are all ECM live data PIDs, it looks like it only reads ECM data. So it looks like the BCM is sending out the Accessory serial voltage and the Wakeup voltage, I posted the case study on the All Data community tech page and only got 1 tech who asked if you were able to communicate with the BCM. I posted the codes and what was happening but surprisingly did not get any other replies at all about it. I know these BCMs in these GMs fail constantly, the last thing to try is wiggling some sections of the harness around. Like the connector for the ignition switch, or any bulk in-series connectors. ECM connectors, etc. I would also take the cover off the BCM and check the actual circuit board for any burns marks or melted IC chips, if something shorted out and burned a trace on the circuit board you'll see it. The last BCM failure I dealt with was a short through the Radio on the Serial Data wire. It was clearly visible on the edge of the board. I was able to solder a trace over the burned section, had the customer unplug the Radio connectors and it was ok and restored BCM functions. That was a 2004. But the new BCM will need to be programmed, and there is usually always updated software versions, which you will need a higher end scan tool to do. Most likely the dealership will need to do this. Most of the time the VIN, mileage, and other stored information on the EPROM chip needs to be transferred over, and if its not readable from the old BCM then the actual EPROM chip is moved over on the circuit board. But this is the only information All Data has on programming.

It will be tough to see much by picture, but something to look for in your case, is cracked solder joints, since this happened after it was running okay, and had time to cool off in between drive cycles. When a solder joint cracks it will open the circuit when the board cools off due to expansion. This is where intermittent issues happen a lot, cracked solder joints are super hard to see unless you know which circuit is acting up, in this case we don't know. Here's some examples pf cracked joints on circuit boards. Most of the time you need a magnified glass to see ones like this. They will close the circuit when hot and open when cooled down. Look for these near the sections of board the go out to the pins of the connector first. Then work your way in. I think the BCM seems to be half working in your vehicle but doesn't seem to be waking up the low-speed network and in this vehicle the BCM and ECM need to be communicating together for the truck to start. And that's not happening. But you do have some scan tool communications on the high-speed bus. That wouldn't be happening if the Accessory and Wakeup signals were not there.

I did finally get a message from another tech about this, He states "Replace the BCM then, Your BCM is offline and not communicating which is the cause of all these DTC."