I am wondering if this EMS service has migrated to the new Lubbock system. Have you tried monitoring this new radio system? Lubbock City-County Mutual Radio System Trunking System, Lubbock, Texas - Scanner Frequencies
The frequency listed in the database is 463.775. It is licensed to a hospital and there are 11 other repeater frequencies on the license. Maybe they are using one of these: KMD374 (COVENANT HEALTH SYSTEM) FCC Callsign Details
Med-Trans has no FCC licenses in the Lubbock area. Maybe they are using a repeater or trunked system belonging to one of the local radio companies.