in my 96 4 door dually what rearend is it cant see anything on the tube.no fill plug on cover its on the left front side.i'm thinking its what they call a 10.25 sterling?my chepo truck mite have just cost more .mite change to a 3.73 if its real bad
thanks

 

Its either going to be 3.55 or 4.10's if thats what your asking. and yes i believe its a 10.25 What rpms are you turnin at 75 miles an hour? If your around 2500 rpms, your 4.10's if your about 2250 your 3.55

 

its a 4.10 for sure.i just have'nt learned how to tell the differnce between a dana 60,70 and stearling 10.25 yet.i think 10.25s dont have the fill plug on the rear cover and danas do.if i remember right. the pin on mine broke the bolt that holds it in and started hitting stuff.
thanks

 

He has a dually, it could be a Dana 70 or Dana 80. Might be a 4.11, 4.56 or 5.13
the only way to know for sure is to open it up...anything is possible with a previously owner truck.
Look at the sticker on the drivers door for the axle codes.