Q: Car stalls at steady higher speeds

My car starts up fine and idles well too. While I'm driving in the city with the warmed up engine, it runs without any problems. However, each time I'm at the highway, I increase the speed and start cruising, but very shortly after, the car stalls out. Then I have to pull over and restart it. It starts back up immediately. But, this happens every time after driving shortly at steady, highway speeds. I've noticed that slow deceleration keep it running at those speeds but the engine would sputter. I checked the fuel pump and it works well. I had the fuel filter replaced. Also, the first shift point is higher than normal. What might be the problem?