Recently retired couple, planning a 4 week cross country trip month of May. We start in Ma, but since are familiar with Northeast, we are interested in stopping to see the sights from the Smokey Mountains Nat'l Park on to La, SF then a northerly route back to Ma. We would also like to travel a bit of Rte. 66., also see Grand Canyon, yellowstone, grand tetons, yosemite and anything interesting along the way. Any Suggestions for routes, places to see, It seems overwhelming. Help! and Thanks!