I am rebuilding my 99 dodge nv4500 5 speed manual transmission. What is the best/correct oil to use. 99 Dodge Ram 3500 4 X 4 with 5.9 diesel

 

SAE 50 wt Mobil Delvac is what I used. It is rated correctly for our transmissions. The OEM fluid is no longer produced. I can tell you that since swapping this fluid in mine that the transmission shifts smoother and get up to operating temps quicker.