Some of the numbers you're talking about sound like fuel trims rather than target air:fuel ratio. Fuel trims can jump around quite a bit. It's how the computer adapts to variances in manufacturing of fuel injectors, variances in reality vs calculated model of reality under current local conditions, etc.
The -100% while coasting down just sounds like the computer cutting fuel while decelerating (no need to burn fuel when decelerating, engine will keep turning without it). That's a normal thing for modern vehicles, although I've never seen -100% trims in my data logs.
Yes, I replaced the head flange gasket when I replaced the exhaust pipe. I think I just under-estimated how much I had to tighten the bolts, and I erred on the side of under-tightening because it would totally suck to strip the threads on the head. I re-tightened, and tightened them more than the first time. The obvious loud leak sound is gone now, but I plan to thoroughly check for leaks to confirm proper installation before I focus on forming/sharing thoughts on how it drives with this new turbo compared to the Garrett. I already experienced previously how a small exhaust leak (pre-turbo) can have a noticeable impact on the performance of the turbo:
http://jeeplab.com/showthread.php?13...ull=1#post3705