Gone up Snoqualmie Pass (2,700' climb) and Siskiyou Pass (2,300' climb @6%) a number of times with 2 persons, luggage and golf equipment at the speed limit with no problems. It will downshift to 3rd gear at the steepest climbs.
Winter Park is about a 3700' climb as I remember but I don't think the grade was that steep.
In the winter with the snow and ice you won't be running speed limit probably.