Have you attempted to place the transmission shift lever in neutral and try to start? A failed transmission range sensor could cause this as the start signal from the ignition switch runs through the range sensor before it goes to the starter relay!
Check the fuses that I have indicated in the illustrations below.
Did you crank the engine while checking for power at the interior fuse also?
Try that with a twelve volt test light and see if power is making it to the fuse from the ignition switch
swap the two relays that I have indicated in the illustration below, and see if it starts
That is telling me that there is an open circuit between the starter relay and the starter, as pin 87 runs directly to the starter, you will need to get down under the truck and locate the small wire that is attached to the starter solenoid! first check to see that it is attached to the starter securely, if it is then you will need to trace the wire back toward the location of the starter relay and look for a damaged wire and repair it, if you cannot locate the open circuit, you will need to access the under side of the relay box and run an (OVERLAY) new wire to replace this one as it is broken somewhere! The only other option is a new wiring harness which is very expensive!