Peak boost reduction

[shmity]

Has anyone experienced a reduction in their peak boost? Prior to my most recent service 2 weeks ago (major, including new plugs) i was hitting 1.48-1.5x100 kPa, now im barly hitting 1.3. Previous peaks were over summer so much warmer air, now im in ambient air of ~10 degrees. Fuel is the same (BP Ultimate 98). Im wondering if there could be a slight vacuum leak or something related to the new plugs? The car overall seems to be a little more sluggish as well.
2016 2.0 GT-S with ~68k

 

[Guvna]

My peak boost has been reduced since I got her dyno-tuned, more power with less boost as its now running more efficiently (not relevant to your question but interesting)
The ECU will increase and reduce boost in different weather temps, if its not throwing up a code it could just be less boost due to air temp. Shouldn't feel sluggish though.

 

[shmity]

If anything it should increase with colder air intake, so i dont think its an ECU adjustment to the boost pressure. I gave it a boot full this morning and I'm pretty sure I heard a faint whistle when it was underload/boosting so it sounds like im chasing a vacuum leak somewhere.

 

[Guvna]

Whack an OBDII reader on it, that’ll tell you if a plug is dodgy. Subies do reduce boost in cold weather because the air is more dense, it reduces by percentages, if it didn’t do this you would be over boosting every time it’s cold. But like I said it shouldn’t feel sluggish. If you don’t have an OBDII reader and you’re sure it is sluggish, I’d take it back to the dealer.