Last September we picked up HWY 20 at Dubuque Iowa from Milwaukee and took that west all the way through Iowa. All the way through Nebraska and as far as Lusk Wyoming then south to Guernsey State park.
It was a very easy, relaxing drive and throughly enjoyed the route. Saw a lot of "americana" if you know what I mean. The road was actually in very good shape. Very little traffic and rest stops were easy to make.
I'd do it again in a heart beat. On the way back (from Reno) we took I80 all the way back. The trip out was way better than the ride home! Hope this helps.
Dan