Did some more data logging today. Have both long term and short term fuel trims enabled and the car ran pretty well. Still got some instability at low rpm levels in higher gears, but I'm getting more and more convinced that this is just going to be the nature of the beast with that new engine. All of the signals I am monitoring are looking right on the money (as best my limited knowledge can determine, anyway). So quite likely the engine just doesn't LIKE low rpms and light loads. As Ricky Bobby would say "I just want to go FAST!"
And I had an opportunity to run boost up. I was on a pretty wide open road and just cruising along when I came over top of a small hill (such as it would be called here in the flatlands) and just as I crested the hill, a truck pulled out right in front of me. So I HAD to pass him. And I figured if I'm going to pass him, I might as well REALLY pass him.....
Intake manifold pressure peaked at 26.3 psi, so subtracting ambient sea level pressure comes to 11.6 psi of boost. So it looks like the new wastegates are holding pressure just fine and putting the upper boost level right in the ballpark for where I want it. I would have been happy with 10 psi, so this is just icing to the cake. Seems like the entire STS system is holding pressure OK and the plastic airbridge didn't even blow apart under full boost.
Still need to look over the data I logged but so far everything looks pretty darn good. No knock retard hits being logged, so timing seems OK, and the "seat of the pants"-o-meter is registering A-OK as well.
Short term fuel trims averaged -0.1 and -0.4 and the long term fuel trims averaged -0.5 and -1.2. Overall lambda from the wideband averaged 0.983. So not too shabby in that department, I think.