Having finally acquired my "always wanted one of those" car, now I'm planning my "always wanted to do that" trip.

Since my kids/grandkids live in Dubuque, I'm looking at an extended road trip -- up to 3 weeks, with enough layover time in Iowa for my children to get tired of Dad hanging around.

My first draft of a route:
Outbound..
Portland -- Boise -- Yellowstone -- Rapid City SD -- Sioux City IA -- Dubuque, with an extra day or so allotted for exploring Yellowstone and Spearfish Canyon/Deadwood/Badlands SD. Figure 7 days total.

Inbound..
Dubuque -- St Louis -- Lincoln, NE -- Cheyenne -- Vernal, UT (via US 40) - Wendover, UT -- Reno -- home, allowing time to drive as much of the old Lincoln Hwy (US 30) as possible. 8 or 9 days on the return.

Is this realistic? Ideally I'd like to take as many back roads as possible, with the knowledge this will cut down the mileage per day. But I'm not in a hurry.

Any can't-miss suggestions along that route, besides the obvious (Yellowstone)?