You didn't say when you are planning this trip but if it's later in the fall you could run into bad weather around Flagstaff, you might drop down sooner to I 10 to avoid that. Stay just east of OKC & Albuquerque and go through at 10:30 in the morning, everyone is at work and it's before they are running errands at lunch. We use this strategy on most big cities and it seems to work well. As others have said Phoenix is another story, very busy traffic, try to get there mid day. Know exactly where you are going, what exit, etc., it's not somewhere you want to get lost in an rv.