2008 Peterbilt 389 Cat C15 ACERT - Backfiring through Intake

I have an '08 389 with the SDP C15. Under heavy pull around 1500 RPM, I hear a distinct 'popping' or 'huffing' sound coming through the air cleaner. It sounds like a backfire into the intake. The truck loses boost momentarily when it happens. I've checked the intake ducting for holes and found nothing. I'm leaning toward an IVA (Intake Valve Actuator) issue or a bad cam. This engine has the emissions-era twin turbos still on it.