I own a 1999, 3500. Recently I have had issues with air in the fuel. I have air bubbles in the return lines on the injectors. I have replaced the sending unit, fuel lines, lift pump, and fuel filter. When I run the truck at an idle or fast idle it is ok, but once I start driving it and putting a load on it, it starves for fuel and dies. When I crack open the bleeder on the filter air comes out. Also when I bleed the air out of the filter like normal it fills up, as well as when I crack open the T by the thermostat fuel comes out. I also have a code po251 which I've heard is related to the optic sensor reading air in the fuel. Any ideas where I should start? FYI the injector pump, PMD ( brand new d tech), injectors are all brand new. As well as a Delphi lift pump.