When I bought my car, it had a modified wastegate, which I replaced. Then the problem went away for a while, but now it's back. What I'm getting is a slight backing off at WOT at high revs. I'm thinking boost is sneaking out somewhere. What do you guys think? Bypass valve? Hose leak? Wastegate acting up again?

Is your computer stock? (mine is not - MTM 1+) The problem is ONLY at WOT and it feels like a SLIGHT stumble/ hesitation, but there is definitely a problem right?
1. Most people say new plugs will cure it - didn't do anything on mine. Make sure the plugboots are OK also.
2. MTM thinks it's my MAF sensor - $400-$600 part and NOBODY else thinks that that could be it - especially since the check engine light should come on and it does not.
3. Vacuum leak - hard to find, but most likely the cause.
4. The software itself - several people have recommended switching to Lehman software instead of the MTM - you do then need to go the RS2 route, which I am doing anyway. Others have had the same issue and say that it is now solved.

Anyway, it's VERY annoying. Note that there is probably a code now telling it to run a bit rich. Pull the plugs and you can see heavier carbon depositis on the core.
Jim
93S4

fixed it completely...

not prolly a solution to this!!!

It sure sounds like it. I do not have access to the car right now so I can't see if that is definitely the code. Can you just post what the solution is to that particular code, then if it is it, I can try to fix it and if not, I can archive a copy of the fix for when that does happen to me or someone else.
Jim

Code 2413:
Mixture Adjustment,
Adaptation limit exceeded,
Symptom: Rich mixture, increased fuel consumption