2002 Chevy Silverado Gas not staying in the lines

If my truck sits for more then 45 minutes, I have to either turn the key, to let the fuel pump run for a little bit, or crank it for 7-10 seconds before the truck will start. If I turn the truck off and try and restart it, it will start right back up, which leads me to believe that the fuel is not staying in the lines. The fuel pump failed and was replaced by the dealership about a year and a half ago. The fuel filter was replaced 15,000 miles ago. I have visually inspected all the gas lines I could find, and could not find a leak of any kind, I also park in a garage, and do not have any gas odors or traces of gas on the floor when it is parked in there over night. While I am hoping that it is not the new fuel pump leaking, is there anything I can check without dropping the gas tank and replacing the fuel pump. Or is there a way to check the fuel pump for leaks, as it cost more then I can afford right now. Also, once the truck is running, it stays running and runs smooth, so I don't think the fuel pump itself is failing. My gas mileage may have decreased slightly (around 1 mpg) but can't say for sure as my commute has changed recently.