hello i have a 2003 dodge cummins. It is my first diesel truck that i have owned. about a month ago it would sputter a single time when i start it. i also will be driving down the road and my fuel gauge will freak out and read empty, even though it was full, and my fuel light will come on. But when the fuel gauge freaks out it usually only last 2 to 3 seconds then goes back to normal. thougt it may be the fuel filter so i changed it but didn't fix the problem. is that my lift pump?