So let me start off by saying I’m completely new to the diesel world and just bought a 99 Cummins. So to start off I’ve been driving the truck for about a week now and everything s been fine then yesterday after leaving work the truck would not shift out of 1st gear, kinda like it was d rating or something. I called the guy I bought it from and he said to just fill the tank and that if it got below a quarter of a tank it would do this. So my question is why would my fuel level matter for it not to shift. He also said that the filters need to be changed and might be why, but I’m not certain at all, again I am fairly new to this platform. Any help at all would be great if anyone has had this happen or might know the specific reason why this is happening