The car is actually really good at estimating range. The built in navigation will tell you what the arrival percentage will be for the intended destination. If you touch the map it will show three additional icons - one of which is the charging locations. From there you can select one of the Austin Superchargers and the car will tell you what your arrival charge will be.
The arrival percentage might fluctuate during your drive, depending on if you're driving faster or slower than the rated speed limit that it uses to determine consumption along the route. If it goes down very quickly you can back off your speed and it will come back up.
You can set the navigation to Austin before you even put it in Drive and see what the arrival percentage will be. Hopefully that'll help ease your range anxiety.
The only way to find out is to do it
With only a few exceptions, ALL Teslas should be able to make it between any two
adjacent interstate Supercharger locations without any problem.