Hi Beerwesley. Welcome to the forum!
This is just thoughts coming from various things I've read through the years. I hope that someone can clarify or completely refute my recollections of how things are going.
The rail between San Antonio and Ft Worth are REALLY congested. Austin wants to build a light rail and Amtrak wants better speeds through there. As bad as I-35 is, taking the train right now is almost hellish.
Anyway, the idea is to get a better freight realignment that goes out side of the Austin metro. Amtrak would be able to do better going through there without the UP congestion. Light rail is also a thought, but that would be electrified and completely separate from any diesel run. Amtrak doesn't piddle in light rail at all.
There are a lot more details - let me think about them and get back to you.