Right, I agree with robynanne about transplant shock. If you can possibly rig up a piece of shade cloth to keep the sun off that tree in the middle of the day, that will help it get through the next month or two of very hot, dry weather. It just doesn't have enough root system to support the leaves through a hot, dry day.
My kids all live in Salt Lake, so I know your weather went from cool and rainy to hot and dry very quickly this year. My daughter moans about it to me daily.
You also need to water deeply in the early morning so the plant has time to take up lots of water before the day's heat kicks in. The key is to water deeply! That means 10 minutes with the hose running on the root system of the plant so the water soaks down well into the root zone. Just a lawn sprinkler will only penetrate down 4 to 6 inches in half an hour of sprinkling and I'm sure you're not watering your lawn every day.
Do you have a thick layer of mulch over the root area? That will also help it keep its roots cool, and retain moisture in the soil for the tree. 4 inches of some type of bark or wood chip mulch would be good. Just don't pile it up against the trunk. Rubber or stone doesn't insulate at all, and in fact it heats up and helps to fry the roots of young trees like that.
