Its hard to tell from what you are describing. My guess is that you are overheating when driving on the highway at speed. If so, its probably your radiator that is blocked and should be replaced asap. Hopefully you havent continued to drive it as you risk damaging your head gasket and overheating your transmission if you have an automatic. You might also research the crank and cam sensors. As Rogoman pointed out, have your codes read. Good luck.