A turbocharger doesn't slip. Sounds more like a clutch issue than a turbo issue. The "bark" is the noise you hear between slow shifts under high boost or when letting off the throttle after a hard pull. This is only a surge of air getting backed up between the turbo and the intake and it forces the turbo to slow down very quickly. The Holsets are pretty tough turbos, but I've seen several broken thrust plates and impeller shafts on them due to exsessive barking on a poorly maintained turbo. There's nothing to "slip" in a turbo, and the bark won't slow you down. Might want to check the wastegate actuator to make sure it's good. Over-revving the turbo because of a faulty WG actuator is a common issue, usually the turbo shudders because the wastegate opens & closes rapidly because of a bad diaphram in the actuator.

You might have a dead spot on the throttle if you have an aftermarket or modified fuel plate, this would cause a surge in boost and a dead spot in the power band, but it would most likely always be there and not just happen out of nowhere. Pump/AFC tuning would solve this.

But to me it sounds clutch-ish based on your description.

 

your clutch slipped!!!!your turbo does not make you move!!!