Thanks for all your suggestions. Our trip is purely recreational, traveling in our 40 ft Allegro Bus MH. My wife an I are in Spokane visiting our son. We are from Buffalo NY. Thought it would be nice to see California and the grand canyon, though have never driven on the west coast. Based on comments the route through Bakersfield, then route 58 to the i40 sounds like the way to go. One other issue will be to avoid wild fire smoke areas. That may be a challenge in August. The alternate route to Butte MT, the i15 south may still be an alternative, though a continued heatwave may make that less attractive.