Need some advice. I have a 2000 Chevrolet 3500HD 6.5L Turbo Diesel. All of a suddent the other day, the truck started to get hesitant. Appeared as if it were something with the fuel. It would run fine once started, but as the truck heats up, it is not getting fuel. Or at least this is what I think. I have changed the fuel filter - same thing. Changed the fuel pump - same thing. Changed the fuel pump relay - same thing. Can anyone help with what might be my problem?????