I first traveled Route 66 in 1969 in a '57 Chevy. We crossed the deserts at night because we had no AC. We hung a linen water bag on the front of the grill. Sure it is more civilized now, but depending on how you travel there are lots of dirt roads and remote places to visit.
Keep your gas tank full. Carrying two spares is not over doing it. Be mindful of your tanks and carry extra water. Be ready for some cold temperatures even in summer at higher elevations. Early September will be warm in the desert. Either camp at higher elev or find some power for AC. You have chosen a good route. Do not hurry.