Maybe the best way would be to tap into the o2 wires to see how lean its getting before misfiring? I have an extra sensor that came with a spare motor that I tried and had the same issue, power mode is fine, lean burn feels like a misfire ( no ping/detonation sound) so much that I couldn't stand it. I put the percieved good one back in and runs fine. Sounds like you need some hard data at this point.
Sounds like you had the same problem. Was it the O2 or a wiring problem?
It was the sensor. I bought the car with a new one already installed and given that I can feel the power going down and can get ~50 MPG, I assume Im getting lean burn. I put the used sensor in and those symptoms came with it. Since your sensor is new, I think the only way to know is to tap into the wires at the ecu.
Here is a link