Sounds and acts like car is out of gas, but it's not.

What is your question?

After driving in city traffic for about an hour the car dies usually at a red light or stop sign. Sounds just like it is out of gas but it cant be because I put in plenty of gas when I started driving. So I add about a gallon out of my portable gas tank and everything is fine again. The car is running very cool as I have a new radiator. When I add that gallon of gas after my car dies it seems like it loosens up a possible blockage. Could this be a fuel filter problem or could my fuel injection be bad. Thanks for your help. dko