Hi y'all

I'm having an issue with my 06 STi. Car is warm, outside temp is fairly low, i'll put my foot down & the car obviously takes off. I slow down and then proceed to put my foot down again and there's no boost and what feels like a huge amount of back pressure. After a few minutes of easy driving the car returns to normal.

Any suggestions?

No CEL's.

Mods;
AVO450
TMIC & Y-pipe
APS BOV
TBE
Fuel pump