Why is my car over heating when radiator works?

I have a 1993 Toyota Camry and about six months ago it was over heating and i had the fan switch, thermostat replaced along with all the tubes. When i get in high speed, especially the high way, it starts to creep up to the hot, so i got off and it cooled down. is it because Arizona is so hot and i have no ac? also it has started not to start on the first key turn and it seems like the rpm's go really high before it changes gears... what could this stuff be?