IIRC you also have a fairly full van of people, too, so your weight is pretty high. I'd add two hours to the projected time from Google Maps, etc. Maybe more as there are a variety of places you'll probably want to stop for pictures, etc. If there's one rest stop not to miss it's Grizzly Creek in Glenwood Canyon. Room for large rigs there.
Going up isn't necessarily the issue. Keeping your speed under control without burning your brakes is more important. Use your gears. The downhill parts from the Eisenhower Tunnel and the top of Vail Pass are 7% grades for something like seven miles. Most interstates have a maximum of 6% grades.
Fill with gas in Summit County as it doesn't get cheap again until Grand Junction.