Texas has got the benefit of their schedule. When they beat Michigan, it was considered a good win - not so much anymore - that that pushed them to the top 3 or 4. As teams lost, they moved up - case in point when Bama beat UGA then Bama lost to Vandy then Tennessee - Texas benefited. They lost to UGA the seventh game of the season and as other teams have lost, they have moved up. They are setting at three because of that.
If they lost to A&M they will drop - where they land will depend upon the score and how the other teams look THAT WEEK. A loss would also remove them from the SEC title game, so no chance for movement - but like the SEC teams that don't make the game, with a host of 2 loss teams there would be movement after the championship games.
If they beat A&M, they will probably see loss number 2 in the SEC game. What if that loss is to Bama? They would have lost to the two best SEC teams they played - while Tennessee split with the two, Ole Miss beat one of them.
All I will say is that selecting 3 or 4 from the SEC teams is going to be controversial given the potential of who beat whom and who lost to whom.