So, update on this one. I was posted overseas for the past nearly 2-years - Leaving shortly after the last reply.
Long story short, I swapped in GTR plugs and that has resolved the issues to a degree - I still get a slightly unstable idle with occasional near-dropouts/stalling, but it doesn't seem to actually stall anymore which is good.
I am still however, battling what I think is either an obscure intermittent boost leak, or a tuning issue.
Cold start performance is excellent, however when warmed up I am getting massive power loss intermittently - say 50 - 60% of the time. I'll be driving, and accelerate and have full power & close to 8psi, the next time I accelerate I will get an enormous loss of power and what sounds like air rushing out the exhuast of the car.
I couldn't find any vacuum leaks, and I subsequently had the intake system pressure-tested at a mechanic's and could not find any leaks either, leading me to believe may be it is all tune-related? Could VVT overlap of some sort be somehow bleeding off positive pressure straight out the exhuast?
I'm also getting a bit of flutter at cruising speeds on the highway (60mph) and sometimes in low to moderate acceleration. I dismantled the BPV and noticed some very light scoring on the cylinder, but also that the BPV spring appears to be cut down (it is not a full spring, and has obviously been cut by a pair of wire cutters), however this cut-spring may be a normal adjustment GTM makes to the stock supercharger spring - I am unsure. Idle vacuum sits at about -11, and the valve is definitely open at idle (no flutter).
What gets me, is the issue is totally erratic. Logging in UpRev is confusing the s**t out of me, I understand the concepts but looking at the ignition timing and AFR's, they are a bit all over the place (for instance at idle I'm getting +125% fuel adjustment, but light throttle I'm getting -90%. I'm also seeing detonation at low throttle across 1500 - 2200rpm in 1st and 2nd, but logging it shows AFR dead on 14.7 (with moderate ECU adjustment), so not sure if this is timing related? I wonder if there are some sensor differences with the AUDM model that screw with Sam's base tune?
I've contacted Sam in the past few days about this, so hopefully I can pay for some remote tuning time - The only UpRev tuner anywhere near me (still >2 hours away) wants multiple-thousands to even take a look.
Will keep you up to date
Sorry for the 2 year delay!