You are missing a lot of information that is necessary for me to help you further.
First, what year is your Durango and what year is your Ram?
Second, what model of Ram is it (1500/2500/3500)?
Assuming you have a 2nd Gen Ram, if you have a 1500, you have the Dana 44 and if you have a 2500 or 3500, you have a Dana 60. The Dana 44 takes SAE 80W-90 where as the Dana 60 takes SAE 75W-90. Also, for the Durango if you have a 1998-1999 you have the Dana 35, and if you have 2000-2003 you have the Chrysler 8.25 (Corporate 8). The Dana 35 takes SAE 80W-90 and the Corporate 8 takes 75W-90.