Have an 03 silverado, started life as a v6 auto, but now is a cammed 5.3 with a t56
I'm using an engine block from a 01 silverado
04 silverado wiring harness
using dbc rather than dbw
I uploaded the base tune onto the computer, but the truck won't crank for more than a split second. I've jumped the starter relay and the engine will turn over fine. I put a new crank sensor and a new starter in it with no change.
https://youtu.be/zTNgPXK43ow
Video of the problem, i was holding the key on the whole time.

 

Vats?

 

vats is disabled

 

I recently did the same thing you did but swapped in a 6.0 with a 4l80e and I’m having the same starter issue you were having. Did you ever find out what caused it?

 

OP hasn't been on since his 12/27/21 post.

 

Just guessing, but it sounds like it's loosing the signal from the ignition switch, to the starter.