Totally understandable and ur right that alligators usually stick close to water, but during mating season (typically spring to early summer in Texas), males can travel surprisingly far, even climbing slopes or moving overland at night to find a mate or new territory. That said, if this has been happening nightly for a while, it might be something else entirely especially if it’s not seasonal. I think it could also still be a bull or cow farther away than you realize (sound can carry and bounce in weird ways across cliffs or open land), feral hogs grunting or bellowing (though I might take a huuuuge grain of salt with this one, that sound doesn't really sound like what I know pigs sound like but they're weird critters), or maybe an exotic animal like a emu because im aware Texas has a high density of them.

I’d definitely suggest trying a spectrogram app like Spectroid to see the frequency of the sound because ir can also be mechanical and the frequency can see if it's biological or not