Ask Mr. Smarty Plants

While we are going to check to see if we can find any diseases of Acer rubrum (red maple) with the symptoms you describe, we're pretty sure we can tell you what has happened. The Red Maple is native in Texas only to the far eastern sections. Here are its Growing Conditions from our Native Plant Database:

Water Use: High
Light Requirement: Sun , Part Shade
Soil Moisture: Moist
CaCO3 Tolerance: High
Soil Description: Moist, slightly acidic soils.

That doesn't sound much like Buda, Texas, especially for the last two years, does it? The soils in this area are generally pretty alkaline, and certainly haven't been moist recently. Now that the weather has cooled and we have been getting some rain, the tree can probably go into dormancy for the winter without permanent damage. However, when it leafs back out next Spring, if we are having the same conditions, you need to be prepared to try to keep it alive with deep watering.

Getting back to the leaf yellowing, it sounds like chlorosis. We learned in our research that maples are often subject to iron or manganese chlorosis, especially when growing in an alkaline soil. This article from Cornell University Noninfectious Diseases of Maples discusses that possibility.

In the final analysis, it would seem that your tree is just planted too far west. It grows most prolifically in Eastern North America into Canada, and the small area in East Texas where it grows is as far west as it is considered viable.  It always pays to check on a plant, especially one as valuable as a tree, to make sure it will be welcome in the soil and climate where you want to plant it.