I have a 2000 dodge ram 2500 diesel 4x4 quad cab automatic with 120,000 mile all original equipment. The truck runs great except for when I'm driving and sloping down to a stop say below 10 mph. The truck felt like its racing and then a hear a banging noise coming from the motor just before you stop. The dealer had it for a week and couldn't find it. It doesn't always do it but I felt it and know when its going to happen and not sure if it is something serious or not. Do you have any help on this?