ISX15 intake backfire ???

[Steamboat]

I have a 2013 Coronado with ISX15, still mandated, that while under load and boost builds I get what almost sounds like a backfire coming from intake. It does it once and boost drops, happens again and boost drops again and then end up having to down shift. Any ideas at what I’m looking at… boost sensor, turbo actuator, turbo… all the above