[GTP Dad]

First of all the sensor could have been bad especially from the old engine. He should have put a new one on a new engine and when he did he should have done a quick case learn procedure so that the ECM would have recognized the new sensor. Takes a couple of hours to change depending on the engine.

I would trust the computer on this one since the symptoms you describe are those most commonly seen with a CPS problem. Whether the computer is new or the old one as long as you aren't experiencing major computer issues it should be fine. New CPS should cure the problem. Good Luck!