Well, as I said, I have no experience with the 6.4. I'm hanging out here because I will be ordering one in the next year or so. With that said, my 7.3 will make a woosh for maybe 5 or 6 seconds between shifts at times and I have a lot lower boost than you. From what you descibe, I don't think you have surge, but these motors may act differently than the older single turbo ones. Hopefully someone who has owned one of the previous engines and has a 6.4 can give you thier opinion. I saw a video a while back in the 6 liter forum of a truck with a serious surge problem. See if you can do a search for it and compare to your truck.