03 Tahoe no crank

The engine crank electrical system kinda fools some people because many assume you are just looking for 12v+ and that is not the case. The starter relay needs 12v+ from Ignition fuse E AND the other side of the coil for the relay is looking for a 12v-(Ground Seeking) which is provided by the PCM once it decides to enable it. For the PCM to enable it there must be 12v+ going to the PCM terminal C2-59 which is provided by Crank Fuse 10a. Since the starter itself works manually, closing the solenoid proves this is a control power problem and not a load (starter) problem. I would goto the starter relay and put 2 wires on the bottom side so you get in circuit measurements while someone is cranking remembering one side is + and the other -. See which one is missing and work your way back from there to see where the open is.

When I need a quick and easy answer about a relay, I just switch the suspected relay with another from another position. In 50 years, I haven't seen very many bad relays but switching positions is easy and quick.