My truck developed a huge fuel leak coming out of the top of the tank. It is pressurized fuel that is leaking. Once the power to the pump is cut the leak subsides. I don't have the time to tackle this myself and don't want to take it to the stealer.

 

The steel lines coming out of the top of the tank have probably rusted through, you will need to either drop the tank or unbolt the bed to get to it.

 

That was exactly my problem last week while I was away from home and my garage, tools, etc. The fuel pump bracket had rusted out and had to be replaced. Problem was noone had the bracket in stock anywhere in the upper midwest and it took 4 days to get the part. I had to leave it at the local dealer in Ohio and grab a rental car.
Don't know how bad your leak is, but I could see the gauge moving when I drove it to the dealer. Be careful.