If you consider the island of New Guinea to be part of Oceania, then Mount Kosciuszko is not the tallest one on the continent, only in Australia proper. And I think the Labrador peninsula is the largest in North America. The Alaskan peninsula does not include the whole of Alaska, just the westernmost elongated tip of the state that continues further on into the Aleutian islands.
I thought the alaskan peninsula included more land than just that, but it seems you are right, so now the Labrador peninsula is included. And about the tallest peak, I´ve updated that as well. The confusion was that the source for the islands in Oceania included New Guinea, but the one for tallest peaks didn´t.