I have a 2006 3500 4x4 diesel dually and have run delo since it was new. It has 130,000 miles on it and I am considering switching to synthetic oil and gear oil. Any thoughts on this and advice for which brand is recommended. The rear diff has 14 bolts, dont know how to find out what size I have. Any help is greatly appreciated.
Thanks in advance

 

I believe your diff oil is already synthetic. Mine is, and I believe they all are. The 10 1/2" diff is 4.75 pts, the 11 1/2 is 7.65 pts.

 

Being a 1-ton you should have the aam1150. The factory fill spec is synthetic. IIRC your truck was perfectly ok with the CI-4 oils, so I'd recommend using a synthetic CI-4+. I'm not a big amsoil fan, but apparently they've got a marine duty synthetic that fits the bill.

 

Thanks for the info. I appreciate it.