I concur...window tinting would be far more effective than the dash cover. I too, struggle with Texas temps, and have found the window tint to be a major improvement! The A/C cools much faster upon startup, and isn't nearly as taxed during operation.

Make sure you don't go overboard on the degree of tint color. There are laws regarding what is legal, and too much tint will fail your car during the annual inspections.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car