I had these same issues. Ended up being numerous broken grounds, corroded negative battery cable wire in the middle of the cable and corroded and broken ecm cable $2000 later, it runs great again.
I brought my 5 month old 2015 Silverado to the dealership I bought it from and was told "surface rust is normal". Funny thing is the 10 year old Silverado I traded in had less rust than the 2015 I have now. I called and made a complaint with GM, hopefully it gets resolved.