US 280 to Denton from Amarillo and then I-30 to Austin
sorry. i was vague. download the waze app. it’s an information aggregator for driving conditions, which can change from minute to minute.
it’s also pretty awesome for finding a route that is quicker, but perhaps you had overlooked.
I-35 is the primary N/S road through central TX. And I would not recommend it as it carries heavy traffic that bogs down regularly. Knowledgeable travelers stay off of I-35 and use parallel roads on either side of it. In the case of the OP, I'd recommend 287 S/E out of Amarillo to Wichita Falls then take 281 S to Lampasas, taking 183 into the Austin area. I highly recommend stopping for BBQ in Stephenville at the Hard Eight BBQ joint. It is right on the highway.
I-30 don't run that way, pardner. You want to get to Austin from Denton, you take I-35 south.