Rotella is a fantastic oil and T6 is the icing on the cake!I have been in construction for over 40 years and I can tell ya that the preferred brand for our heavy equipment (dozers, loaders, excavators and such) has always been Rotella.  And now with T6 you just get more of a great thing.  Tried and true and may they never stop making great diesel engine oil.I get mine at Walmart for 21something a gallon.  Not 100% sure, but swear I get an extra 1mpg in my Duramax now that I switched over to the T6 from the regular Rotella T.  Best part is my cost only went up by about $8 a gallon - or $20 an oil change.  Knowing that most engine wear happens at start-up and that synthetic holds the edge with cold circulation abilities, I love being able to switch over to synthetic for so little money.*******************************************************************************************************************************************************Edit:  Wanted to add that I spoke with Shell Tech Support to confirm that T6 is fine to use in all ambient temps.  As some may have noticed, it is a 5W-40 and if it were a conventional oil you most likely would not want to use it in a hot climate like Vegas.  But being full SYNTHETIC, there is no issue whatsoever - IT IS GOOD FOR ALL CLIMATES.  Oh and he was able to confirm too that I can absolutely use it in my Honda Goldwing as well.  However, NOT in any engines that call for 0W-20.  Just an fyi for yas, the 0W-20 requirement of some engines is not to be played with as there are tight ports that could otherwise easily be clogged by any higher weight oils.  Deviate from that at your own risk.And finally, with the $5 rebate they keep running, my Duramax oil changes are now only about $8 more using Synthetic T6 over Regular Rotella Triple T.  And I "can" extend those oil change intervals if I wish.  Awesome!  Love this stuff.  Oh, and they claim a 4 year shelf life, but that has more to do with liability over future oil advancements than it does with oil "spoiling".  Mobil 1 claims 5 years.  Keep the lid closed tightly and store your oil between 32-100F and use it within 5 years and all should be good.One last note about SYNTHETIC OIL so as to be clear that I do not make a blanket statement that it should be used by all.  There are certain benefits that synthetic brings with it's higher price and if you feel these are something that you want then use it.  They are:* Better cold starts when MOST engine wear occurs.* Excellent cold weather pour-ability and lubricity.* Slightly better mileage.* Longer engine life (mainly because of the better cold starts), however, maybe ask yourself when's the last time you ran an engine to death.* You "can" go with longer engine oil change intervals simply because synthetic tends to take longer to break down than conventional.  This can offset the extra cost of synthetic; doing less oil changes.