[Kim473]

With the altitude change, you should be able to take to a dealer and get ( assuming computor controled ) computor reprogramed or something like that.
Google search it on the net.

From what I searched, you lose about 3% hp every 1000 feet, and you probly best to just change the prop. As, if you go back to sea level and forget to adjust the fuel mixture back you can burn your engine out. Ask a dealer and like I say maybe just change the prop.