2015 5.3 lt issue

i have a 2015 lt 5.3 that has been swapped into a 51 chevy truck. it has a current performance wiring harness. The truck will run as long as you are on the throttle, but will not idle. It also throws a code for loss of communication with ecm/pcm. but will start and die if you are not on the throttle. The engine has a texas speed camshaft and valve spring upgrade. im not as familiar with the lt based engines and operating parameters as i am with the ls. Any ideas on what could be causing this? or how to fix it?

Welcome: Be sure and attach your tune and log file of the events so you can get help. And a little explanation on how you are getting fuel to the high pressure pump.