I've done quite a bit of troubleshooting on the car and searching online for solutions to this problem, so I am hoping that someone can point me in the right direction.
Starting about a month ago, my LGT has had a sudden "loss" of power. This is accompanied by a "whoosing" or "sucking" noise under acceleration. Off throttle, there is no noise. On throttle, it is a constant and heavy "SHHHHHH" sound.
The motor itself is has the stock airbox, with silencer and all OEM components, and a new air filter. Factory BPV has no leaks and the o-ring is intact and solid. Intercooler does not have any noticeable leaks that I was able to detect. And the coupler to the throttle body appears to be sound.
There is no check engine or dash light that has appeared, and the car starts and drives fine under boost and does get up to speed, just without any "motivation."
The turbo itself is building pressue, as the BPV and turbo make the "normal" sounds (we installed an aftermarket BOV and invidia downpipe today - lots of turbo whine and ricer bov pops, did not solve the issue). The turbo has no shaft play, and spins freely.
Any exhaust leaks were addressed, and doing an "soapy water spray" test did not find any other intake leaks.
I'm starting to think that something is going on with the drivetrain - i am getting a bit of noise when the clutch is depressed and in neutral. Possibly the throwout bearing? It definitely also needs a new passenger front axle, but I doubt that would cause this noise.
Any ideas or places to start? I feel like I've gone over everything at least twice to no avail.