Echoing what others from Texas have said, thanks to the Texas Motorist Protection Act, you are not required to have a permit to carry a firearm in your vehicle, loaded or otherwise. However, if you do so sans permit, the firearm must be concealed. That can be as simple as throwing a jacket over it in the seat. If you don't have a permit (known as LTC in Texas), then obviously nothing is going to come up when they run your DL so the officer probably won't even ask. Personally, I would inform them that I was carrying, just so they'd have all the facts and proceed with the traffic stop accordingly. You don't have to just blurt out something like "I have a gun", but rather something like "Officer, I would like to inform you that I am carrying a firearm in my vehicle". Then he would probably ask where it is and just tell you to leave it there, then proceed with the traffic stop.