How do I actually lower cooling costs in this heat?

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Cooling load in the US 75 corridor from McKinney to Durant is dominated by the attic, and the order of operations is different from a heating-dominated climate. Where the load comes from. A dark roof in full sun drives attic air temperature far above ambient. Anything in that attic, including the ductwork and the air handler in most houses here, is sitting in that heat. Duct leakage and conductive loss in an attic is a large, invisible, and continuous penalty: air leaving the register several degrees warmer than it left the coil is cooling you had already paid for. The order that returns the most. Seal and insulate the ducts, or better, bring them inside the conditioned envelope where the design allows. Air seal the attic plane at top plates, penetrations, and the attic hatch. Insulate to current code depth. Then consider a radiant barrier, which reflects radiant heat from the roof deck and is meaningfully effective in this climate specifically, unlike in northern markets where it is often oversold. Then look at attic ventilation and at shading on west-facing glass, which carries the afternoon load. What about the AC. Replacing a functioning system with a higher-efficiency one produces real savings, and it is usually the most expensive dollar-per-unit improvement on the list. Doing it before fixing the ducts means sizing and paying for a system that will keep pushing cooled air through a leaky attic distribution system. On metal roofing. A light-colored reflective metal roof does reduce cooling load and it lasts far longer than asphalt, particularly against the hail exposure here, where some homeowners see insurance credits for impact-resistant roofing. Payback is driven more by longevity and insurance than by the energy line. The measurement worth buying first: a blower door test and duct leakage test, which puts numbers on both problems and tells you where your money goes.