There is no Harris County in Virginia.
The agents could have sent a text to Gibbs or anyone else. Text messages will often go through when voice calls will not since they do not require as strong of a signal. Bishop being technically proficient would know this.
Torres could only get a signal when his phone was held outside the window, but he could have typed the text first, then hit 'Send' while holding his phone out.
The pressure plate in the prison is held down by the closed door. Then, when Bishop opens the door, she steps on it to keep the bomb from detonating. She could have stepped out and closed the door which would have held the pressure plate down again.
NCIS pulls GPS data from cars to see where their suspects were all the time. Surely their own car has a GPS, maybe even a dedicated GPS tracker to locate it. When they found the car, they should be able to see the locations it went to.
Bishop and Torres did not leave their car running. Presumably they did not leave the key or fob in the car, either. So how do the bad guys start the car and get away? Kasie says the car was "hot wired", but this is not possible with cars made after the mid-1990s or thereabouts.