I agree that you should talk to the vendor/breeder. I live down in San Marcos, TX and I've driven with my snakes back and forth from several areas in that type of heat with no problem. This seems like he had something going on before the car ride, especially since the other two were fine. How much did this guy weigh?
Also, what did you transport him in? In this weather a tub that is closed without holes can heat up very quickly.