Whenever I drive my car up a significantly steep.

Whenever I drive my car up a significantly steep incline, and the gas tank is either at half or below, the car dies as if it ran out of gas. Once it gets over the hill however, it runs perfectly fine. Also if I drive the car up the same incline with more gas in the tank, it runs fine as well. I am wondering if it has something to do with the fuel pump, or the sensor? I'm not sure but I'd like to get it fixed so that I can take it out of town.