The Truckers Mountain Directory (link given above in another post) is highly recommended if you're driving the western highways.
It gives lots of information on the 'problem' roads.
For I-40 in Arizona, the only notation given is for 10 miles EAST of Ash Fork for WESTBOUND traffic: "6% grade next 6 miles".
For I-40 in California the only notation is for SOUTH PASS/MOUNTAIN SPRINGS SUMMIT - west of Needles, CA and reads as follows "The EASTBOUND descent from the summit starts with about 2 miles of 5-6% grade and then goes to about 3% for about 5 miles. The WESTBOUND descent from the summit is about 4-1/4 miles of 4% grade. This climb is about 5 miles long and gradual most of the way".
I-40 will not be a problem for you. Good travels!!