have a safe drive down - I recommend going south to Sioux Falls, 1-90 West to Murdo, 83 South to North Platte, I've driven this route since 1995 and found it to be the most pleasant with the least amount of traffic and nicest scenery (no black hills, but that slows you down anyway).
Gas up in Watertown or Brookings, Murdo, North Platte (don't get gas near the interstate exits if you can help it, I've saved over $.25 gallon by going to the middle of town in NP).
You should make Denver in ~12 hours @ 80-85 MPH, plenty of places to stop along the way, watch for cops in Nebraska on 83 as you get close to North Platte, SoDak is not so bad for cops.
Go Sioux! we'll be watching on the big screen. I would love to go, since it's only two hours away from home, but there is just no way possible for me to make it happen this time, next year though...