This "power loss," is pretty much the throttle not opening up as wide especially under 3k RPM. Or you'll get a surge after 2k RPM. This happened when I was stock, and seems to have been remedied by replacing one of the brake switches. I still get this problem occasionally as well after a cold start, or after driving for long periods of time. The car sounds different as if it is subdued, so it's obvious the throttle isn't opening up as wide or opens up at a slower rate as the driver commands it.
This is the one thing I don't like about DBW systems since the ECU is constantly optimizing for efficiency. One thing you can test, though, is to rev it past 3k RPM in 1st (no need to floor it), and then in 2nd you'll feel the throttle response is much different.
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