ISX15 cm2350 boost surging around 60mph

[TomHanson]

To start out with, this truck had this issue prior to any repairs I have made. For reference, I have built dozens of these isx's, so I'm not leaning towards any of my work being the issue. Not to say it can't be lol. The engine was demandated about 200k ago. I am not sure if thats when the problem started. The driver in it at the time did mention a power issue, but he was kind of an idiot. So we chalked it up as that. Once up to temp (and under full acceleration) I can watch the boost gauge surge from 28psi down to 10ish psi and back up again, all within a second or two. This will keep happening until you let off the throttle. The engine has nearly 1.1m on the clock. Tore down for a full rebuild since the head gasket went on one of the last trips. Included in this rebuild was an oem turbo/actuator, head, all rockers and shafts, exhaust gas pressure sensor, boost sensor, 6 pack of oem injectors, low/high pressure pump, you name it. Essentially the only things that are original is the ecm, harness, lift pump, and rail relief valve. I am curious if its not in the programming itself. Is there anyone that can take a deep dive into this current ecm calibration to see if something is off?? I will try attach a data log of all parameters of when the engine is acting up. Edit - I should add, I've test about everything you can test. There is no fault codes. No issues on fuel pressure side, and I have tested the fuel system for about everything you can do. CAC test fine, no boost issues 7th gear and below. Ran exhaust wide open before any aftertreatment canisters, still the same issue. I'm sure I'm missing other tests I've ran as well. Any help would be appreciated.