First off, are your oil levels and coolant levels fine? Check with the dipstick and visually to verify. Either way, you don't want these low in that kind of heat.
Secondly, yes, it could be vapor lock.
Third, make sure the quality of gas is high, ie Chevron w.techron.
Fourth-In that heat, I would be using Mobil 1 15W-50.
Keep us advised what you find.
