My handbook for my 2004 2500 says no need to change the oil in the 6 speed manual transmission. I bought mine new and it's never been abused or jerked around. It got to where it didn't want to go in gear at a stop....wasn't grinding like the clutch was bad, just very hard to get in gear. Also didn't like going into the next gear after getting it rolling. I found some You Tube videos about the problem and they said change the oil and it would fix it. Also said to remove the shifter and overfill it one quart from there instead of the fill plug on the side. I did all that and it went right back to shifting like butter again. I'm beginning to wonder if whoever wrote the handbook is