The typical symptom would be the vehicle dying when you put it in reverse or drive with the brake pressed, or if the brake is not on the vehicle would move on it's own, at a faster rate than considered normal..Typically a locked converter would just cause the truck to die upon gear change to P or R..
Let us remember the purpose of a torque converter. When the truck is moving slower than it should be relative to gear selection and engine speed the torque converter opens up and slips; similar to a clutch being halfway depressed.
At a stop, the torque converter takes all of the engine speed and dissipates the energy by spinning the turbine in ATF.
If the torque converter is stuck in the locked state when you come to a stop you'll stall, just as you would if you didn't press the clutch in when coming to a stop.
Remember also that the torque converter -should- lock up when you are not accelerating. When you're on the freeway and you give it some throttle to accelerate you can feel the tranny pretend to downshift, almost a half gear downshift but definitely not all of the way into third. That is the torque converter opening up. Press the pedal further and it will shift into third