Ok well lets see here! Engine was running normal you say and all other gauges were functioning correctly. I'm assuming fuel flow was indicating, otherwise you would not have a running engine. In your situation I would of guessed the gauge too! But since you say it wasn't after the swap then your looking at an ITT harness most likely. Or at least something happened to the harness. Most likely to change that you have to pull the engine. This is all I can hypothesize with out being able to ring the harness out with a meter. If this is not right, dont tell me the answer. By the way what model engine? I might need another hint though if I'm wrong. I might have another guess if this is wrong, but that guess would entail replacing the harness too, along with some T wheels.