how would you know if you have a 8.25 or 9.25 rear? is one a 3.55 and other 3.92?

 

8.25 has 10 bolts 9.25 has 12. i'm pretty sure all the 05 and up dakotas have 8.25 rear's.
3.55 seems to be the most common ratio. if you look on the front side of your axle there should be a decal that says what ratio. also, the window sticker says if you still have it.

 

And it says it in your glovebox as well.

 

i have the 9.25 corporate rear with the 3.55 in my 05

 

Mine is the same way. I just went outside and checked.

 

I have a 12 bolt 3:92

 

I did the same thing, after I didn't find it there I looked everywhere in the truck I could think of for that sticker and finally gave up and called the dealer with my VIN #.

 

If memory serves, it's on the top of the glovebox... I can't recall where I saw mine. At least, mine was in there.

 

I just went out and double checked...I was curious whether I missed it the first time or not. I didn't. There's nothing there.

There are no stickers on either of my doorjams that give that information either.