You might be experiencing a fuel cut, not a boost cut as such, maybe your tuner should try and dial a bit of boost out down low to avoid this, although if your on 100% wastegate duty cycle and still having boost control issues, you may need to look at other alternatives, a boost controller wont do any more than the Xede in these terms.
My understanding is that the Xede can scale the boost cut higher than your peak boost and the wastegate solenoid adjustment controls the boost, fuelling is then adjusted to suit the new boost profile.
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