Actively hunting down the cause of my 4k RPM hesitation/rattle. I have narrowed it down to the SSV not actuating as when the vacuum chamber is disconnected from the intake, the rattling goes away while experiencing similar hesitation along with .8 lambda under load past 4k. done multiple smoke tests on every vacuum related component, no leaks. swapped the ssv solenoid connector+vacuum line onto the air pump solenoid/position with 0 difference made. The car only throws air pump+downstream o2 codes due to air pump delete+racing beat midpipe, no other codes ever. vacuum pump+gauge coming in this weekend to bench test the solenoids and take a live reading of the vacuum being experienced between the ssv and solenoid at the actuation point during a test drive.

Lambda currently drops to ~.85-.95 on load past 4k rpm, as well as my STFT jumping to +10% at 4k but leveling out as the car is pushed whilst not solving the power loss/rattling. If all the solenoids pass the bench test, and vacuum is still not being received consistently to the ssv, am I safe to assume it is a wiring fault? there are 0 issues under 4k rpm, under load or cruising. fuel trims steady at -7%-0%, lambda steady at 0.9-1.0 both under 4k RPM. idle smooth at 850 RPM.

Related parts already replaced:

-ssv+solenoids(solenoids may have been cheap from what I remember but confirming operation this weekend)
-fuel injectors rebuilt and flow tested
-fuel pump from a known running car
-suspected cracked vacuum lines
-maf o ring
-ess sensor
-spark plugs+coil packs

I can add pictures/videos if helpful, thank you.