I started reading through the post you sent, but not the whole way through everything yet. My symptoms are not quite as bad as his. I have some basic datalogs from recently and I don't see any Wastegate symptoms like his. My wastegate typically changes to 1 in first gear and right around peak boost drops down to .75-.65. Seems pretty normal to me.
My boost levels are not too abnormal. Right now I am battling some boost drop issues in my E30 tune, but running the 93 custom tune I will see spikes around 17-19 at max. I'm not sure if this is too high or not honestly with how these cars control boost. It tapers down right after as I would expect.
When I see this problem happening it tends to be at very low boost. I don't even have to be steadily increasing throttle for it. Like I said I can replicate it with cruise control on a small incline.
I have checked and tightened all connections I can access and have not found a problem recently. When I first got the car I had some boost problems with the one line coming from the boost control solenoid and the clamp on the TB was so loose it almost came off. These were causing surging and my boost levels going up to 22psi. These were fixed before I ever noticed this new problem.