Fly higher too. Getting a few thousand feet higher where the air is much cooler can provide much more relief. Sometimes the piston guys seem very apprehensive about going up more than 3-4K, and at low level in the summer in a hot climate, you just get beat to hell in miserable heat when you stay low. I know it doesn't help with the ground, but it makes it easier as an entire flight. I also would never choose to fly out of somewhere like PHX, Texas, etc., for this reason. Just too oppressive in the summer IMO.