About an old thread AT vs MT gas mileage

[LSTurbo321]

I recently read the thread posted about the gas mieage between At and MT cars. I'm curious because as i said before in my old posting "O2 sensors" my car was converted from AT to MT and the person who did it left the ECU from an AT car, now would that affect gas mileage as well? I've also heard a rumor from some people that a car i.e. a honda that is MT with an ECU from an AT would have more power, now i consider this to be total BS but i just want confirmation from you fellow honda drivers that it in fact IS BS.