I may have made a really dumb mistake. I started a business of hauling cars with a chevy Duramax 6.6L diesel with no mechanic skills whatsoever. Ha Ha. Never done an oil change or fuel filter change in my life. I want to start doing them due to the prices dealerships like to charge and the lack of knowledge they have (to say the least). I pull 32,000 Lbs. with a gooseneck hitch. At what mileage intervals should I do the basic preventative maintenances.

The following is the schedule I have received as of yet looking for more advice thanks so much.

4000 Oil change/Oil filter/lube chassis/check fluid levels
8000 Above plus fuel filter change
12000 4000 maint plus air filter cleaning and re-lubricating (K&N Filter)
16000 8000 Maint
20000 4000 Maint
24000 12000 maint plus flush transmission fluid/change differential fluids

Hope you are not using K&N with the LMM.

This sounds like a maintenance thread. Not an engine specific thread. Let the thread titles be your guide! ;) Moved!

With pulling that kinda weight I think that you should look into changing your rear diff fluid right away.

If I was you at 4k I would collect an oil sample and get an UOA, and depending on results you might be able to take the next drain interval out an extra 1000 miles and recheck, continue to do so until you reach a point when the oil has had enought. Then you know how far you can take the oil with the abuse that YOUR truck gives it. Now understand that different oils will last differently, so 15W40 Rotella T might not last as long as say 15W40 Delco.

How difficult is it to change the Rear Diff fluid? Any body willing to give me a very good step by step directions or know where to find some. I am pretty much clueless. lol

Not hard at all, drain the diff, refill through fill plug to about 3/4" below the bottom of the fill hole when diff is cold. Make sure you are on level surface for accurate reading. Towing that weight, I would run 75W-140 gear oil, recommend Mobil 1 fully synthetic. However, if you are where it gets really cold in the winter, you may want to rethink that or possibly change fluid out to 75W-90 before winter sets in. The 140 weight will not flow as well when cold but will provide better protection/lubrication under hvy load when it is not very cold.

Rear diff takes around 4qts. Should be able to drain out of bottom bolt on diff cover without removing whole diff cover if you have a recent model year, I think. I know that earlier years required removal of diff cover, but can't remember exact year.

X2 on not using a K&N filter with your DMax

http://www.dieselplace.com/forum/showthread.php?t=198162

Good step by step with pictures...

http://www.dieselplace.com/forum/showthread.php?t=116418

This one even better. Look under the DIY section for more.

Kevin