I think TPWD stocks the park near the town of Blanco in December or January -- put-and-take winter rainbows. The only year-round trout in Texas (other than a small wild population way up in the mountains, way out in far West Texas) is in the Guadalupe River. As hot as it has been, your best bet would probably be the first couple of miles below the Canyon Lake dam, and though it is not my thing I've been told nymphing is the ticket. There is public walk-in access there.

Plenty of other great fish in the area!