Disclaimer: The worst conditions I ever ride in are about 95 degrees with 70-80% humidity. Any more than that, and I tap out. You might be dealing with worse conditions in Alabama.
But the only thing that’s worked for me, even among UPF shirts, is Patagonia Capilene Level 1. Ironically, it works better for me if it’s long sleeved, which seems counter intuitive when conditions are really hot. But I get heat stroke and heat rash easily due to sun exposure, so having more of my body covered is optimal. I wouldn’t normally have thought to buy Capilene since it’s better known as an insulating base layer (Capilene Levels 3 and 4), but a backpacking friend pointed out that Capilene Level 1 is designed for super-hot conditions and encouraged me to try it. I bought mine from REI, which has a no-questions-asked return policy within the first year because I wasn’t convinced that it would work. Let’s just say that after a week of wearing my first Capilene Level 1 shirt, I went back and bought another one.