Hi, glad to be of help. It does sound like you have a fuel pump problem, however a fuel related problem will usually chug like not getting fuel shortly before dieing and a ignition module,crank sensor or ignition switch will simply quit without warning. Being that you only have 50psi, key on engine off, you definitely need a fuel pump. Replace your fuel pump & fuel filter. I would start there. I have had the same thing happen to me where it works sometimes after sitting awhile and may go for days before it happens again. Check your fuel lines and hoses for cracks, rust or corrossion, but the botXXXXX XXXXXne is the fuel pump is failing. Check to make sure you are getting a full 12 volts to pump and check to make sure battery is in good condition and fully charged.
It would be easier to drop the tank than to remove truck bed but that's up to you.
Here are some videos that show how to do both. It also shows where the hidden bolts are on truck bed removal.
Video-Fuel pump replacehttp://www.youtube.com/watch?v=LXRGj2vOeS8
Video-Truck bed removal
http://cardealerforums.com/alt-trucks-chevy/t15854-2000-silverado-remove-bed-drop-gas-tank.html Read last line.