when you say no power, what do you mean? you say the idle is normal, shifting is normal, no codes, no external symptoms... what makes you feel that the power is lost?

you press on the pedal, does the engine react? the RPMs go up with the pedal? or, you floor it, but the RPMs are barely going up to 1500-2000? could it be the air supply is compromized? check the MAF, the air hoses, the throttle butterfly...

how about a vacuum leak? when you pop the hood, any strange noises?