Every time I run my truck for a long time the fuel pump fuse blows. I was told that something is touching but no one seems to know what. Could you help me?

If you could measure the current of the pump, you may find the pump has a problem.
You could unplug fuel pump and verify no continuity with the chassis(ground).
May only happen when driving, a bump or something may make it touch where sitting still may not.
Intermittant problem can be tough.
A good place to check current may be the fuel pump inertia switch, may be on the side kick panel on passenger side.
These switches open on impact. You could unplug, plug in an Ampmeter and monitor as you are driving, and keeping eyes on the road. Or have someone else monitor.

It may also be something as simple as a bad fuel pump relay (worn contacts), located in the under hood fuse box. Most likely, however, it's an internal problem with the pump motor. If you end up replacing it, install a new Motorcraft fuel pump. Disconnect the negative battery cable, after properly depressurizing the fuel system, before beginning work.

I have replaced the relay fuse already and it is still doing. It started blowing on the back tank and then now it is blowing when I use the front tank. Are there 2 pumps one in each tank and will I have to replace both!!