This weekend I replaced the differential fluid in the front and rear of the 06 3500. I used Amsoil 75/90 Severe Synthetic. I simply pulled the covers off and I was able to reuse the flat rubber gasket. On the front, I had to lift up the left side of the truck frame to gain access to the differential bolts,( suspension bars blocked it.) otherwise, I could not access the bolts. The simple lifting of 4 inches allowed me to easily get the bolts off and to re-torque to 30 lbs. Front diff took 3 qts and rear took 4 qts. There were 14 bolts holding the cover on. I know I read a lot of posts about this process and I thought I would share my experience.
JB