Originally Posted by sgaston
I'm the original owner of a 2007 2500HD Classic 4WD with 65K miles. All other maintenance has been kept up to date, but I haven't replaced the differential and transfer case oil. Should this be done soon? If so, should I use a synthetic for longevity?
First welcome to DP
I’m still the Original Owner of our 07 Classic for another month and I have all the Owners Manuals including Diesel Supplement Manual.
6-14 Page 550 of your Owners Manual
Front & Rear Axle
SAE 75W-90 Synthetic
(GM Part No. U.S. 12378261, in Canada 10953455) meeting GM Specification 9986115.
Yes, I would use Synthetic of your choice since it recommended.
This might help
As for the transfer case I filled through the top fill not the speed sensor that some recommended. I figured it wasn’t necessary.
There is a debate on what oil to use in your transfer case on here. If you want me to find it I can or you can do a search