i have a 2019 chevy silverado with a 5.3 engine with 166000 miles that the lifters and cams needed to be replaced so i purchased a 5.3 out of a 2020 silverado with 16000 miles when i swaped the motors i used the wire harness that was on the new motor but when i went to start it it was flashing several different issues on the screen and would not start when i pushed the button to turn it off it said it was in gear but to shifting handle is in park a mechanic told me i had to use the original wiring harness so i swapped it and had the same problem wont start i had a mechanic come out and reprogram my computer now it shows in park and the starter throws forward but does not spin

any suggestions for me ?

 

can you jump the starter solenoid, see if it will crank, go from there.

 

Welcome to the forum.