If what my high school auto shop teacher told me is correct, you loose roughly 10% HP for every mile in elevation above sea level you are at. You are naturally going to loose some HP the higher up you are, so I doubt it has anything to do with the ECU.
As for break-in time or requirements, there ain't much. Machining techniques and precision are so good now, there is very little required to break-in an engine. The most important thing is that the rings seat properly. I believe the owners manual says don't tow or drive at constant speeds for the first 500 miles, and go easy on the brakes for the first 200 mile so they seat properly. The owners manual does NOT call for an oil change before 5k miles so doing that is overkill IMO. Other than that, just drive it. :driving: :biggrin2: