if you're pretty restricted on your days you can take off from work(like me), an alternate plan that may work for you is to fly out to Missoula on a one-way ticket, spend a couple days with your sis and rent a one way vehicle(van or sedan) in that area for a much more(8-9 day maybe?) leisurely drive home with time to see some sights and enjoy the time with your family. Some of the extra costs this would incur would be made-up by the mileage(approx 5-6000) and wear & tear savings on your truck.