So I've done some snooping around but cant find any specific answers to what kind of fluid should be used for rear diff fluid. Some say one thing, some say another, then some say an additive needs to be added depending on if you have a limited slip or not...Sooo im confused...how do i know what MY pickup needs for fluid?? Someone posted that your VIN will say what you need...how does that work??

 

Sorry, ive got a 2004 1500 with the Hemi

 

Tccards500. I have the same truck. 75-140 for the rear. I use only sythetic, but that is up to you. You only need the additive if you have limited slip diff. Mine does not. You can change the fluid, no additive. if it has LSD the rear will chatter when turning. Or your local dealer useing the VIN # can tell you.

 

There's usually a sticker on the glove box door that will have "... anti-spin differential ..." on it. If the sticker's gone, there's an easy way to find out.

75W-140 is what most of us use, but if you don't tow, 75W-90 is OK. It was born with synthetic, best to use that on the drain/refill.

 

9.25" Corporate diff is what these 1500's have. They take ~2.25qts of fluid. This is equivilant to 2qts of fluid and 1 bottle of 7oz modifier.
Since most Synthetic fluids come standard with modifier in them, you don't need to add anything additional, but 75w-140 is like $20 per quart, so you could cheat and add 2qts of 75w-140 and a tube of modifier. It'll save you like $13..haha
I added 2.25qts of Mobil 1 Synthetic 75w-140 and have the remaining .75qt in my garage for the next time, which is what I would reccomend you do as well.