Gasoil circuit air

Hello everyone, since you helped me once with the injection pump—and how! You provided the solution that even the mechanic couldn't find. I'm back with another problem, as stated in the title. I have an ISUZU NKR crane (it looked like the NPR, and it's also listed as a Chevrolet), and the problem is that air is getting into the diesel fuel system. I've changed the filter twice, and the base where the filter screws on three times, but nothing has worked. Every time I use the bleeder (bulb), a lot of air comes out (I checked with a clear hose). I even tried connecting it directly, from the diesel tank to the pump. It seems like hardly any air is getting through there, but the jerking continues. I also noticed something that might be odd, but the return line also has air coming back in. The crane starts and accelerates fine, but it jerks, and I think it's because of the air. I changed the hoses and installed... New ones, it's as if air accumulates in the tank and when it passes through the pump it's expelled under pressure.
This is the crane


And this is the filter holder.