Mebz, thanks for that! Gave me some confidence in my original suspicions. This definitely sounds right on, the ARV is just dumping my boost pressure at improper rpms due to a worn out spring.
Considering doing an EGR delete...
This thread shows deleting/bypassing some of the wiring associated (first time I've seen anything about doing anything more than just replacing it with a plate/cover). But first I'll try and get that ARV closed off. Doing some more homework on the EGR in the meantime.
On the bottom of that u-shaped plastic duct that goes from filter housing to turbo is caked and wet with oil on it's underside near it's ends. I've read that this is normal for high-milage engines, can someone tell me why this happens? Is it coming in from the dirty EGR air?
This little blog post seems to be a decent brief rundown of the EGR, ARV and ALDA and why people get try and rid of them.