P0327?
You need to get ATAP on there and check for knock retard and see what your timing advance is running. Timing Advance running lower than noremal is the PCM protecting you while High Knock Retard is a sign of a mechanical problem or faulty sensor.
These two readings will point to your loss of power and potential drop in mileage. I don't know if the PCM has a protect mode that might be in play when one of the knock sensors goes bad? This could be your loss of power as the engine pulls timing to reduce the risk of damage from an undetected Knock problem.
Things to check electrically before replacing the knock sensor would be engine sensor fuse and verify that the engine ground wiring is secure (2 wires on back of driver side head to one bolt, one more wire to another bolt close by on the back of the driver side head and one wire on the driver side head by the engine temp sensor). Checking the knock sensor wiring requires pulling the intake off to get at everything as the wiring exit from under the intake at the rear of the block.
Here's an excellent link if you get to that point:
http://ls1.fbody.com/
Rick


