You must remove the supercharger and manifold to replace the knock sensor. If Nissan does it you're looking at $750-$1000 P&L to do it. It's a real PITA! Mine just went out too. With a supercharged engine you gotta replace the sensor. The power loss you'e feeling is when the knock sensor goes out it retards the timing and bypasses the blower. The sensor is located on the left bank between cylinders 2 and 4.

A P0328 is a bad knock sensor code