More than likely it needs water in the original rootball.

That can be true in spite of any watering/irrigation that's been done.

To know for certain, stick a finger into the original rootball.

"(I) planted a good sized C.M. tree last month."
You picked the very worst time of year to plant a tree. It's best to plant most trees and shrubs in fall or early spring. Planting in mid summer forces the plant to deal with the stresses of summer heat without an established root system. The immediate problem with your tree is probably a combination of what Jean proposed and the fact that the plant's root system is not equipped to handle the stress it's going through.

"...and added some soil amendment w/added Miracle Grow for good measure."
Adding soil amendment when planting trees and shrubs is not a good idea. Studies have shown this to be detrimental in most circumstances. It discourages proper root growth and can cause soil drainage problems. You should skip this step with future plantings.

From my observations dealing with crapemyrtles that don't do well after planting.

1. Be sure it's getting enough water. Crapes are water hogs when getting established. With regular watering (light and frequent) you'll notice they can go longer without water as the season goes on.

2. Be sure it's not planted too deep. I've seen too many trees that are planted or mulched up on top of the root ball. The root ball should be visible after planting, and above the ground about a couple of inches. As little as an inch of soil on top of the roots can be detrimental to crapes.

3. As stated above, amendments don't do any good unless used on large areas, such as the whole yard or beds.

I don't necessarily buy into the spring and fall planting only. The truth is, if planted correctly and sufficient irrigation provided, summer plantings will see very fast root growth. Too many people think that since they planted in the spring or fall, they can afford to not irrigate or only do it sporadically. Obviously, if you live in an area that have definite wet and dry seasons, you plant in the wet season. However, locations that receive regular rainfall on average from month to month, plantings can be done year round, unless the ground is frozen or the plant species requires a specific time.

In the case of crapemyrtles, mid-spring through the end of August is the optimum planting period. There are now some recommendations by some growers/researchers to not plant crapes after September 1, since it supposedly increases the risk of cold injury the following winter (that can be said for any borderline cold hardy plant in your planting zone).

The problem with planting in summer can come about before the roots develop. There are a number of factors to consider here. For instance, if the tree or shrub is potted (which Bookert's crape myrtle likely was) there is often less transplant shock (because there's less root loss) than would be expected from bare root or b&b plants. But, even with potted plants, the likelihood of transplant shock goes up with root disturbance. If the plant is potbound and the roots have to be worked or if improper handling leads to unnecessary root disturbance, sufficient root mass, to prevent problems with summer heat, may be missing. If one assumes that the crape myrtle was potted, that it was not potbound, and that it was properly handled, then summer planting should be perfectly fine. Maybe a better way to look at it is that spring (or in some cases, fall planting) can be advantageous for non-ideal circumstances.

Optimal planting times vary with climate, but, in my opinion, spring (or fall, in all but the coldest growing range) planting of a crape myrtle would always be preferable to summer planting if other factors were the same. For Fall planting, risk of cold injury the following winter would definitely not be an issue for crape myrtles planted in southern California.

A huge thanks to all who posted!

The tree came in a huge wood box structure and the soil was very dry when taken out. We opened up the root ball gently as it was pretty compacted. The root ball is not showing and we may have planted a tad too deep!
Will post more soon!

sheesh...I'm having the exact same problem!!