I did a 1500 mile trip last year in heat ranging from 95 to 103. Here are some tips:
Know your fluid absorption and sweat rate. If you sweat faster than your body can absorb fluids, you will be inclined to drink, but the fluids will sit in your stomach. You will begin to feel bloated and nauseated. The cure is to slow down and reduce your sweat rate and let your body absorb fluids. Keep drinking. When you are thirsty, it is too late.
Don't be afraid of salt.
Be in shape. If you lost alot of weight on your shakedown trip, you probably weren't in good shape.
Wear light colored clothes. I found Under Armour to be the best. It doesn't stick to your body when you are sweaty. Cotton bad.
Have a base tan. Sunscreen wears off quickly. You need some natural protection. Keep piling on the sunscreen anyway.
If you are camping, use a tent with good ventilation. It will be hot in the tent at night. You don't want to wake up dehydrated.
I don't tolerate heat well. However, on my trip I was amazed how my body acclimated to the heat. The body is amazing when it wants to be. I was in shape and at the end of ten hour days in 100 heat, I never felt spent at the end of the day. Pace yourself accordingly. Take lots of breaks and enjoy the scenery.
Don't be concerned. Prepare yourself and you will do fine. Challenges are why we do stuff like this.