Thuck has 33000 miles and reading new manuals see that it should be changed. Pull front cover and lube looked about right. Pull back cover and lube look like tom cat p#%@. What ever happened to good old gear lube we used to have in differential. Would think that a truck with trailer tow package would have better lube in from factory. I would recommend every one to change differentials and put in a good lube. I'm going to 80-140 sythetic. Got my exhaust brake Friday . Oo. Ordering gauges monday am. Will be busy next weekend with all the installs. Thanks for the good site to learn all about our trucks. Its opened my eyes to things that should be done and checked. Time to go to work, see you later.