Yeah, but not nearly as much as with carberation. With efi and ecm, the computer, with the help of the map sensor, can adjust the air/fuel ratio to achieve the ideal 14.7/1 ratio, whereas with a carburator, the ratio is set by the jets and your altitude at that time and is not adjustable automatically. Of course greater altitude equals less oxygen, and therefore, less potential power, but at least with efi, its not as nearly as bad due to the computer's ability to regulate the fuel/air ratio.
Although only anectotal evidence, I had to floor the 89 jeep in second gear many times to make it up to the alpine visitor center in rocky mountain national park (approx. 11.7k), whereas more modern vehicles with efi were simply cruising on up.