First off..Modern Mopars are not real receptive to "trick of the week" spark plugs, Put in it what is supposed to be in it (IIRC RE14MCC4) and before the crap starts...if anybody has trouble believing me on that...come do my job for a while, this isn`t my first rodeo
Second, have them..or somebody clean the throttle body, Good...do not just wipe it out, remove it and clean it good, it must be spotless

While they are there pop the map sensor out and make sure it dosen`t have alot of buildup on it.


And yes some of the early 5.7`s had a tendency to break intake valve springs, It isn`t so common that every one does it, but it happens.

Just my

Rick