You'll want to program in Pecos DPS, which is heard on 155.4525 half duplex (mobiles on 154.7025), 159.2175 Alpine repeater, and 158.8200 repeater in southern Brewster county, which is the Big Bend area. All communications in West Texas are P25 digital full time, non encrypted, as is most of the state at this time. Basically, here is the deal:
DPS dispatch centers located across Texas primarily dispatch on one of four half-duplex, but repeater capable, channels:
A1-155.4600, mobiles on 154.6800
A2-155.4675, mobiles on 154.6875
B1-155.4450, mobiles on 154.6950
B2-155.4525, mobiles on 154.7025
Additionally, they may control one or more (some up to five) outlying repeater sites to be able to dispatch a wide area, such as Amarillo DPS does for the entire panhandle. These outlying repeater sites are mostly on 11-19A (159.210, different digital NACs) or 11-19B(159.2175, different digital NACs). But as you can see from West Texas, several non-standard repeater sites are out there also, such as the 158.820 repeater in southern Brewster county. You can find these non-standard repeaters scattered throughout the database. Also plug in 156.210, which is a chit chat channel for Commercial Vehicle enforcement officers.
The database might be slightly confusing, however the only confirmed dispatch channels in use are at the top of every dispatch center's box. The database lists EVERY LICENSED channel just in case. You will also see 159.0900/159.0975 and 155.5050/155.5125 listed either in digital mode, or analog PL 162.2 with available DES encryption. They are used by the Criminal Law Enforcement division, not highway patrol. As a matter of fact, many HP units do not even have these channels in their radios. The CLE division includes Narcotics, Auto Theft, works with Feds, and many other functions. So to recap:
Highway Patrol:
A1, A2, B1, B2, Repeaters A and B, and non-standard repeaters.
Criminal Law Enforcement:
155.505/155.5125 and 159.090/159.0975
Commercial Vehicle Enf. Chit-Chat
156.210
All divisions and dispatch centers:
154.950 car to car, or statewide Texas Law 1 (can talk to just about any sheriff/police here)
155.370 intercity, or statewide Texas Law 2 (every DPS and most sheriff/police dispatch have this on to talk to any unit in state needing interop)
155.475 national, or statewide Texas Law 3 (good luck hearing anything but bleedover from A2, 155.4675 on this channel, they just don't ever use it)
Also, since you are in Brewster County, DPS may also talk to the SO to help answer calls on 155.655 and 158.790, or Alpine PD on 155.1225.
Have a great trip, and don't forget to scan the Federal band from 163 to about 170 to catch Border Patrol, Park security.
