Do you have the power loss also right after you crank it up? even if its just for a minute or two?
Try disconnecting the Mass Air Flow Sensor, and running with it disconnected. If dont feel any more power loss, well then its the MAF Sensor.
You will probably get a rough idle, and a check engine light while unplugged, but you will feel the difference in power if it was bad.
If you reconnect the old one back in or put in a new one, the idle will return and the check engine light will go out.
Just a quick suggestion to try!!!