01 Sunfire Won't Start

01 Sunfire won't start, it just turns over. It has been doing this for about 6 months. The first time it happened it had about a 1/4 of gas in it. I disconnect the fuel filter and turned the car over to see if it was pumping fuel and it was not. I hooked it back up and waited til the weekend to fix it thinking the fuel pump had gone out. The weekend came and it still didn't start so i jacked up the rear of the car and started to disconnect the lines. The fuel line was pressurized so i hooked it back up and it started and ran great. I dropped the car and drove it for sometime. It has happened a few more times since then, and each time the car was above 1/4 of a tank and had as much as 1/2 a tank of gas. We figured out that if we add a few gallons of gas it will start up and run fine. It just started doing it again and I want to fix it this time. I dropped the tank and pulled the pump. I inspected it and the tank for any debris that may be causing a blockage but everything looked fine. I hooked everything back up and it still won't start. I don't want to replace the pump unless it is absolutely necessary because if it is not that then it will be $250 down the drain. Anyone have any ideas?