I was driving down the interstate after about 6 or 7 miles I couldn't get up to speed. Then the car started to sputter and wouldn't shift properly. Eventually I couldn't get the car past 50 miles an hour. The car idols fine and starts. It is not leaking anything. It ran fine in the morning going down the interstate shifted fine and ran perfectly normal. The day before it kind of did the same thing as this specific time. It was around 100 degrees out at the time. Could this be vapor lock or maybe a fuel pump or fuel filter?