I have recently purchased a 2500HD 4x4 with the Duramax Diesel & a 6sp tranny.
A recent post asked about synthetic oil. I personally recommend Red Line. You can see their products at
Red Line will tell you that you will get better fuel economy with their synthetics. This is true, at least for me. While I found no mileage improvement using a synthetic in the engine, I do get 2mpg better using the synthetics in the trans, transfer case, & differentials.
I have used Red Line synthetics in my cars (sports cars) as well. I have noticed the same mileage increase using the synthetics in the transmission & diff.
My opinion on oil changes: I believe oil changes should be done when the oil has sufficiently deteriorated in quality. I believe there is no benefit to changing more often than the manufacturer recommends unless the oil has worn out. The question remains how to determine this? Does the oil life indicator in the truck help? In my cars, at least, I find I can double the manufacturer's recommended oil change interval without the oil deteriorating in quality if I use the Red Line synthetics. I still change the filter on schedule, but I double the oil change interval itself. You may argue with this, but what's the problem if the oil is still of sufficient quality to allow this?
Now, I'd sure appreciate some advice:
Where is the best rpm to drive at for best fuel economy?
Admittedly, I am a first time buyer of a Duramax with a 6sp. Where would you recommend shifting to the next higher gear for a no-load condition & for a heavily loaded condition?
When I use the engine heater, can it be left plugged in all night long, or would you recommend plugging it in 2 hours before I leave for work in the morning?
Dave