Is this always from a cold start or always from a hot re-start - or just any old time whether cold or hot?
Any of the basics that you learned in the fleet mechanic training apply - at least for initial troubleshooting. Unfortunately you do have to just wait for it happen to keep diagnosing. Personally, I would rather an actual fuel pressure gauge on the fuel rail rather than taking reports through the electronic gizmos. If you don’t have a gauge, a lot of the auto parts loaner tool programs do have them. You will need to look up the correct spec. If it’s supposed to be, say 55-65psi, then 40 isn’t good enough. (You might need to know if its a Vulcan (12 valve) or Duratec (24 valve) engine as the spec could be different).
I would also want to have a can of starting fluid around. If you blow some into the intake and it gets it to run a bit then you can be pretty sure that you need to stay on fuel. If the fuel pressure at the rail tests good when it won’t start, but starting fluid gets a cough out of it then you want to look toward power for the injectors.
And the other thing is spark if you don’t get anything from the starting fluid - so you’re on the right trail. Having a spark tester is the easiest thing.