I have a 1994 Pontiac Grand Am with a 3.1L V6, Automatic Transmission with 134,000 miles. I recently had the radiator replaced and am soon to get the lower intake gasket replaced. I've noticed after the radiator was replaced (about a month later) the car started to, what seems like, go into neutral when I stop. That is, occassionally the car will feel like it has gone into neutral and when I press the gas the engine just revs and then it jolts and goes back into gear. It drives fine and goes through all the gears fine but every once in a while (usually after the car gets really warm or its a hot day) it tends to (what feels like) go out of gear and go into neutral and then jolt back into gear. But I have noticed it only does it when the temperature gauge climbs or its a hot day. It does not have this problem at night or on cool days (until the car gets warm). The problem occurs multiple times on these warm days or when the car gets warm.