Well that means your Vgt is for sure staying closed, or not opening enough, over boosting and running extremely lean. Insane amounts of back pressure... So far every symptom you've mentioned I've seen exactly the same with frozen tubes. So I'm still a leaning towards frozen catalyst pipe and/or tube. I know you replaced it and cleaned it but it only really takes a drop of moisture to plug off the tube. And as I said before, The low part of the catalyst pipe fill up with water over time from the exhaust and has no where to go. Eventually it will completely cover where the bp tube connects. My best advice right now which would scratch off a bunch of variables and maybe solve the problem would be to remove the catalyst pipe, drill and tap the block off plate, move it up to where the catalyst pipe use to come off the up pipe, install the the bp tube and sensor into the drilled and tapped hole in the block off plate. Not only will it take water/debris buildup out of the equation, but freezing all together regardless of temperature.
If you do that and you still have issues, the vgt actuator is the most likely culprit hands down.