I've been having this problem for over a month now and it's driving me insane! The car was running absolutely mint before and all of a sudden the car feels very sluggish. I noticed that I get anywhere between 16-18 in 3rd and 4th. But once I get on the highway it only boosts 12-13 and it feels like I'm going nowhere in WOT. I've smoke tested the car and didn't find any leaks. Here are the parts I've changed this past week:

N75 - brand new
N249
Put forge 007 Diverter valves
TBB
O2 sensor (mine was lazy, no CEL just a code every time I scanned it)
Drivers side intercooler (mine looked like it was soaking, so I changed it)
Mass airflow (Bosch) brand new

(I have a spare motor so I just started throwing things in)



I am running out of ideas. Any help would be really appreciated!