We just took the trip from Maine to California (original starting point was New Brunswick, Canada). We travelled the I40 for most of it. There are a few places I would never stay again....in Albuquerque NM, don't stay at KOA next to Camping World. There is a resort on opposite side of highway....beautiful.
If you are going to Grand Canyon there is a KOA called ? Pines where you don't want to stay. Their rates are high, and they truck in water daily and will not hesitate to tell you not to use it. But please go to Sedona while taking your trip. Go through town to airport. There is an area there that is just amazing. I enjoyed Grand Canyon, but Sedona was much nicer (in my opinion). Same rocks just younger than Grand Canyon.
We stayed at KOA, Amarillo - had a blast at the Big Texan Steak Ranch. We had so much fun there, we did it going out and coming home. We also spent time in Holbrook AZ doing a few day trips .... Oatman AZ is a real neat little place. Only time in my life that we were chased out of town by donkeys! Route 66 was on my bucket list and when we hit the end of it, we were at Santa Monica Pier so we had to dip our feet in Pacific. We have officially been shore to shore since the Atlantic is in our back yard.
Would do it again in a heartbeat. But just retired 1 year and the dollar exchange is gonna be a killer for us. But we had a great trip, met up with old friends and made some new ones.