I am in SC, too and I have never seen that on a crape myrtle.
You might want to try posting your question over in the trees forum. Someone there might be able to help.

Wezzie,
Looks like alphids to me.
Most modern cultivars of crape myrtles that the nurseries carry today are very resistant to pests, but you don't know the situation that the tree has been growing in.
To get rid of the alphids, you simply spray the tree down real good with a hose now, and when it starts leafing out in the spring.
A nice hard spray on the tree is about all you will need to get rid of the alphids.
Alphids have many natural predators that will be out in full force to battle them once the weather warms up.
You will see wasps, and other predators that will keep the alphids under control.
Keep and eye on it, if you see the leaves of the tree becoming distorted, spray again with the hose.
Try to use the hose, not to kill the natural predators that by mid sumer, will be all over your tree, eating the alphids.
If you see alot of ants under or near the tree, go buy some Amdro at a local big box store. Sprinkle all around the bottom of the tree with it, and apply again whenever you see more ant nests.

Hello! Did you ever find out what this was? This is the only picture on the internet I could find that matches the spots on my maples!!

The black spots are not aphids at all. They are small growths that are part of the fungal growth (grayish splotches) which will soon partner with algae to become harmless lichen.

The nursery might have an issue with lichen on other plants and the spores have spread. Growing conditions may not be ideal at the nursery, as well.