The EBPV if stuck closed, would cause a real power decrease and sound like a rushing air sound, kinda like the potato in the tail pipe thing. A couple free easy check would be to unplug the sensor above the water pump and try it and you could also unplug the valve actuator so that the valve couldn’t be electrically commanded to close. The actuator plug is under the turbo pedestal at the front of the pedestal, pretty easy to get to and unplug. Again all this applies to my E99, there are some differences in the pre98 trucks but I think these things are similar.
There are lots of pics of the internals of the turbo and engine and many other parts in my signature picture link below if it would help you to see some of this stuff.