When I fill up my gas tank it leaks from the top

1995 Mazda B4000 this is a common problem with the Mazda filler hose it does rip and causes leak, A replacement filler hose will be needed, I found the best way to tackle this situation is to remove the bed, You will need to remove the bolts that hold it down they are Torx, I belive but not sure its a 55. As those four are removed you will need to remove the electrical connection at the light and also the the filler neck, and have a assistant remove the bed backward to access the filler neck for removal, the installation is reversed of removal, There is another way and that is to reach in there with a 1/4 extendsion and a 1/4 swivel and 5/16 or 8MM socket again 1/4. And manuver your way in there. With fuel cost on the rise its always a good thing to repair any leaks

I agree with the idea of removing the bed. I have done several trucks that way. Once removed, you will have full access to the top of the fuel tank to inspect and locate the leak.