I have a 2015 half ton WT with a 5.3. About a week ago it started cutting off while I was driving it. It was like the switch was turned off. After a second or two it would restart on it's own. I checked grounds and fuses and reseated some connectors and it got better for one trip to town, but on the next trip to town it died and I haven't been able to restart it since.
I replaced the battery about a month ago because the original battery failed. It ran fine after the battery change.
I have removed and cleaned every ground I could find, and rechecked all the fuses. All good.
When I turn the switch to run, everything comes on as it should. When I go to start everything goes totally dead. When I release the key back to run it all comes back on and the gauges all cycle just like when I first turn it on.
In the fuse box under the hood, the run/crnk relay #64 has 12v at the contact side but isn't getting a signal voltage to close the contacts. I can close the contacts manually and it powers up everything downstream - ECM relay, stater relay, and the fuses related to it. With the relay held closed I can start the truck and it will remain running until I release the relay.
I did replace the ignition switch but it didn't make any difference.