Jeez, what a pain this has all been. Over a year I've been trying to track this issue down. Well guys, I FINALLY found the real problem. Just as I thought, there was an issue at one of my ECU connectors, but replacing it did not completely solve my boost problem. Bought an ECU (thanks Grnsky!) just to see if the problem was my ECU all along, and sure enough it was. Car has been running better than it ever has. Thanks to all who tried to help. It's been a huge learning experience, considering all the work I've put into tracking this sneaky thing down. I'm a happy guy, and so is my z!