Thats wierd, when mine shifts at wide open I loose a pound or two, I always figured it was because the rpms where droping off on the shift and my turbine was slowing down with the dropoff in rpms. I've never gained boost on a shift though.
Your D5 will do a great job of pulling in 3rd gear. A higher stall would help spool-up and 60' times. You most likely have a wastegate issue. Did you port the hole in the housing to match the puck size of your downpipe?
Like has been mentioned. It's the increased load causing the boost to raise. If the wastegate hole isn't enlarged the issue will be more drastic.
Thats wierd, when mine shifts at wide open I loose a pound or two, I always figured it was because the rpms where droping off on the shift and my turbine was slowing down with the dropoff in rpms. I've never gained boost on a shift though.
If you have excessive rpm drop, this can cause what your seeing. The other issue is the factory wastegate system. It's not known for it's rock solid boost control.