You really have to be careful in the extreme heat - it can be dangerous if you overdo it - there's a reason they came up with the siesta.Try to do all of your hard outside work early in the morning and late in the evening. From noon 'til 6 pm, we try to stay in the barn with the fans or in the house with the air conditioner, or take advantage of that time to run errands, shop, etc... It may take a little while to get used to, but you might learn to enjoy it. If you absolutely have to work out in it, drink lots of water and some Gatorade too, and take lots of breaks. I very highly recommend a straw hat - if you don't wear one, you'd be surprised at the difference they make. Working in a truck or tractor with a/c is alright for us, but it's harder on equipment and burns more fuel than running in the cooler times of the day.
I can't stress too much to be careful - the heat really can be dangerous.