A friend of mine just bought a 90 Firebird with a V6 and automatic trans for $1000. Car is in EXCELLENT shape. I haven't driven it yet, but I've rode in it when it's doing this... Ok so the problem is..he'll be cruising along at say, 45 mph or so. He'll tip in on the throttle a little bit, and the car will jerk violently. When he lets off on the throttle, it kicks sometimes too. I told him it feels like his torque converter lockup is acting screwy. Is there anything else that could be causing a kickback THAT bad? Like a driveshaft u-joint, or a bad trans mount? It doesn't 'thunk' when he steps on the gas from a standing stop, but the trans does feel very rough and vibration-prone. Thanks.