And if your going the whole drop the tank route to change the sock, and if you haven't replaced the fuel line from tank all the way to up in the engine area away from the rust, do so now. My first 6.5 was in a burb that used to be a paramedic response rig. The dept that owned it was having the same issues with thiers and it ended up being rust pin holes in the line behind parts of the chassis that you could not see. And it wasn't leaking fuel or even wet with fuel in that area. But it was crusty enough that is was sucking air. Any diesel will be intolerant of air in the fuel. A good solid leak free fuel line to the IP and return line to the tank is very important.