The design of the fuel tank is somewhat interesting.
There is a skid, and the skid is welded via spot welds to the tank. The tank skid is what is attached to the frame. You already know this much I'm sure
If you drill out the spot welds and separate the skid from the tank, then you will see that there is some kind of rubber and foam mastic between the fuel tank and the skid. This stuff traps moisture and will cause both the skid and fuel tank to corrode and rust.
There are several ports on the fuel tank. The first is the main fill port, located at the rear of the tank. Above that is the relief port. Both the relief port and the main fill port should be connected via fuel line to the fuel filler neck. The intent of the relief port is double. The first is to allow air to escape the tank while filling. The second is to start flowing fuel into the top of the fuel filler neck in order to signal the user that the tank is full.
The top of the tank has two ports. The first is the port for the fuel pickup/fuel sender assembly. The second is the return line port.
If you have a leak that gets worse when you accelerate, I would first check the connection of the fuel filler line to the main fill port and the connection of the fuel filler line to the relief port. These are to the rear of the truck and therefore would experience leaks as the fuel shifts to the rear of the tank during acceleration.