I-5 through California to Bakersfield to I-40 east to 64 north is 1520 miles of awful traffic and road condition.
For a more pleasant drive and shorter miles (1370) take WA I-82 to I-84 Oregon/Idaho to I-15 through Salt Lake City/Provo and you can then take 2 different routes and amazingly, both are the same mileage:
1) UT89 south of Provo to Kanab, Utah to 89A (which will take you past the North Rim of the Grand Canyon) to 89 at Cameron, Arizona. Take 89 south to 64 west (coming into the South Rim from the east). This is a gorgeous drive and our favorite.
OR
2) UT89 south of Provo to Kanab, Utah to 89 into Page, Arizona. You will encounter an excellent detour beyond Page to cut off a landslide of last year. The detour is newly paved and a good highway. Continue on this detour to reconnect to 89 south to Cameron and pick up 64 west to the South Rim.
All roads are RV-friendly!
Have a good trip!
Full-Timed for 16 Years
.... Back in S&B Again
Traveled 8 yr in a 40' 2004 Newmar Dutch Star Motorhome
& 8 yr in a 33' Travel Supreme 5th Wheel