So I have a 1985 6.2l diesel Silverado k10. And I’ve been having this issue for a while now to where it gets into the 3rd gear before overdrive in my transmission which is a 700r4, the truck will be running and get close to around 45mph or maybe even slower then the truck will just die. I don’t know if it is a vacuum problem with the transmission or engine or a fuel pressure problem. I would be grateful if anyone had any information on how to possibly fix this issue!