We are heading out Memorial Day weekend in the same direction,though we are heading to Oregon,with many stops along the way. One piece of advice would be to avoid Chicago any day or time. Makes Boston look like a merry-go-round. Rt 90 through Indiana is congested,but alternate routes are in dismal condition. Lots of used car parts along the curbs. Long climb out of Mississippi basin,but very different and a great experience. Don't miss the Badlands,and a side trip to Devil's Tower is worth the ride ( don't forget your climbing gear and ropes...not!... You can actually watch people scaling it. Bring binoculars.) Wall Drug...meh.Corn Palace...glorified flea market.IMHO!