I have a 2014 2500TS on the Chevrolet platform. I replaced, starter, batteries, ignition switch but intermittent no start condition remained.
Finally i replaced the Crank and Fuel Pump relays. No problems since. The fuse box is inside the engine compartment on the driver's side near the wheel well. The legend is under the lid to the fuse box.
A bad crank relay will cause a no crank, no turnover, dash lights off condition. A bad fuel pump relay will let the engine crank but it won't start. You likely only need one or the other and you can test which one by swapping them with each other.
I bought this bag of 5 of them and now carry 3 spares, the original starter, and original ignition switch (since they were fine in the first place).
Good luck. Let us know if it works. I have done many mods to my 2500TS and know it inside and out.