I routinely deliver motorhomes to our Sacramento store from Tucson. I, and many other drivers have tried many routes the following is our favorite. This route is very motorhome friendly.
I take I-10 to Quartzite, then north on the 95 to Parker, then the 62 west to Vidal Junction, then north on the 95 to I-40 near Needles.
An alternate, and just as good, is I-10 to Blythe, then north on the 95 to I-40.
Take I-40 west where it becomes the 58 (just west of Barstow). The 58 will take you into Bakersfield where you can go north on either the 99 or I-5. Watch that the 99/58 intersection is under construction and the 99 might be your only choice, as it was last August.
Both roads merge into one at Sacramento. Then take I-5 north to your destination.