Have you ever been driving your car and suddenly it starts losing power? No matter how much you mash your accelerator the car still slows down? There are several things that come to mind in this situation. The most obvious is that the engine is not getting enough fuel. A dirty fuel filter could cause that, so could a weak fuel pump. Another thing that could cause fuel deprivation is a faulty fuel tank ventilation system. When the system that captures fuel tank vapors gets plugged up, it can create a vacuum in the tank, which can starve the engine of fuel. Another likely cause of your problem could be in the exhaust system. If your catalytic converter is partially plugged the exhaust inside the engine might not be able to get out when you're traveling at high speeds. And if the exhaust can't get out, there's no room in the cylinders for new fuel and air to come in. And voila! The car stops running. Have your mechanic start with the fuel filter because that's easy and cheap. Then check the converter, the fuel pump, and the fuel tank ventilation system in that order.