Can anyone help me find out if Texas requires a dishwasher air gap, or if a high loop is all that is required?

You will have to call your local building department for that information but most of the country gives you a choice. In the Tampa Bay Area we use a high loop. Good luck, Tom

Can anyone help me find out if Texas requires a dishwasher air gap, or if a high loop is all that is required?

You didn't specify which city in Texas.

But, for the most part, the state of Texas has adopted the IPC, which gives you the option of either an air-gap or a high loop.

OTOH, given the frequency with which municipalities amend the code they've adopted, it would be worth your while to check in with the local authority to determine their expectations.

Can you tell where I can find this exact verbiage in the IPC?
Thanks!