Buddy, you said two things in this thread about you being an electrical engineer and an old school mechanic. .. instead of testing with $5 tools from harbor freight, why aren't you using a digital multi meter? I get mine out every time I have an issue like this.
Also, old school mechanic, try putting your foot down a notch while cranking. (Flood your carb) tell us if it runs longer than 4 sec. If it does, it's probably throttle body.
Also, after you got it to run and die, cycle the key with a one minute pause in between cycles. Listen for the pump. My pump on my 2015 GT is loud enough for me to hear from the driver's seat.
Do you hear any clicks every time you cycle the key? No clicks, replace the fuel pump relay in the fuse block under the hood.
I don't know about your generation car, but is there a second fuel pump on the frame somewhere that accelerates the pressure up to 50psi? My old 89 bronco did.
Try all that and let us know
2015 Mustang GT Premium with Track Pack (i think calling it the performance package was just dumb)