Welcome to the forum. I looked at the starter circuit for 5.3, all the fuses for that circuit appear to be in the underhood fuse box. The yellow wire goes from the ign switch to the crank fuse underhood. I'd check the circuits at the starter relay, underhood fuse box. Voltage for the coil side of relay is hot all the time. Voltage for coil side of relay goes hot with the key in the crank position. Any testing you do at the relay, make sure the tranny is in park or neutral and the e-brake is set.

As far as communicating with the computer, check for voltage at pin 16 of datalink connector, that terminal should be hot all the time, if it isn't hot, check the cigar fuse circuit.
This guide will help
https://www.2carpros.com/articles/starter-not-working-repair
and
https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing
Please run down these guides and report back.
May 19, 2021 at 2:36 PM
(Merged)