Any reason for the only 3-4 days? Years ago I drove across country form NY to LA via the North and down the West Coast for 23 days to get my friend to grad school. NY-CHI was the first night. A lot of driving in 1 day is boring and takes a toll on the body. We broke it up into a vacation even stopping in Spokane Washington to see some of my family after 4 days in Yellowstone on our way to Seattle before heading down the coast. I suggest making it into a bit of a vacation. Find a few sites a couple of hundred miles apart and let the good times roll.