In your Log the dropping Airmass I believe just shows your torque management kicking in.
I don't believe that is dropping trans clutch pressures at all.
I would like to think its all predicted to drop during the shift.
I'm pretty sure you car was not Super Charged originally.
So If your Virtual Torque Model was never adjusted it would almost have to be off.
I'm also not sure how much the early E38 relied on the Torque model for transmission calculations.