We plan to get started in mid-May, and the trip will be about 5 weeks, which will include the leg from SD to NC. It is a pretty aggressive schedule, but we are going with two other families, and with that dynamic, there is always different "must sees," time considerations with additional families members flying in/out of big cities in the middle of the trip, and other details that needed to be worked around. Two families will be pulling travel trailers behind trucks, and one will have a van pulling a pop-up.
We plan to stay two nights in most locations, with Lake Powell and Yellowstone being exceptions to that, staying 4 and 3 nights respectively. All of the reservations have been made through the Yellowstone leg with the exception of Salt Lake City since I haven't found "just the right spot" there.
In terms of roads, we are open to either interstates or more scenic routes, but with the time schedule, interstates may make the most sense. Our biggest concern with roads is really staying away from narrow, windy, no-guardrail mountain roads, although fewer trucks would be a bonus, so thank you RoyF for that suggestion.
Thanks for your help!