If you decide on I-40 all the way across drop south from Amarillo on I-27, than take US 60 into New Mexico, then US 70 across the state. Good four lane with virtually no traffic all the way to Las Cruces. Then drop a couple of miles down I-25 to I-10 and into Arizona.
When we go that way we stop at
Trailer Village in Roswell, nice folks and a nice little park. Then we stop at
Fort Wilcox RV Park. which makes for a short hop into Tucson the next day.
There is also a self serv car wash in Ft Wilcox that has a big bay that can handle the truck and fiver.