The coaches can change mechanics pretty quickly. I think the Texas coaches have done a fantastic job of that. For all the whining and kvetching in previous season, Texas players are well conditioned and athletic. Obvious.
What they can't do is make the team mentally tough in one offseason. Right now, they're fighting at least 4 seasons of fighting to hang on. If Texas had entered the 4th quarter down 5, we'd have won the game. However, the crazy large lead so early in the game put the team in rare air. OU knew they had to pick up the pace and bear down. They were expecting to win, and worked to see how it would happen.
Texas didn't know what to do with their good fortune. They'd staggered the champ with an early round head shot, but didn't know how to see to the rest of the game. When things changed and momentum flipped (it's going to happen almost every game), Texas lost their cool and couldn't get it back.
The only way to become mentally strong (no one really wants to believe this is a thing in sports, but it may be the most important thing) is to be there, do that, and know you can handle it. Texas is going through that process.