Problem 1: shuddering on tight turns, first thing to try is an auto trans flush, after the flush refill the box with DEXRON 3, then add a friction modifier. it sound like the transfer clutch is sticking/binding. If that doesn't work, you may need the clutch replaced.
Are your tyres the same size front and rear? They must be or this tight corner braking will occur.

Need more info on boost control.

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F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i