Wally - not knowing which county San Antonio resides, I didn't look it up in the db - however, 2 possibilities exist;
a. If it's a 400 mhz system, you need to program the base/offset to trunk properly. If you can scan the system conventionally and hear traffic, then this is likely to be your issue -or-
b. If you hear no traffic, that's an indication of what has been happening at military installations nationwide- they're moving to 380-390 Mhz, which your 996 will handle. The Texas forum, and others, would be the place to go for information on that.