First - welcome to the site! I should have said that earlier. This is a great place to learn and contribute.
Second, as a fellow Dmax owner, along with others here, I can assure you that synthetics used at "normal" OCIs is a total waste of your money.
There are hundreds, thousands of UOAs showing that conventional lubes will easily survive 10k miles, and more at times, under extreme use. These UOAs also show that, compared to synthetics, there is no benefit to using a syn for these "normal" OCI durations. You won't see less wear, or cleaner PC counts, etc by using syns for short-to-moderate durations. The OLM in your Dmax is fairly accurate. If you follow it, or change oil even before that, you're going to be just fine using a conventional oil, and save a LOT of money.
You can easily use a 10w-30 year round; I do, and so do others. It is not the "preferred" grade, but it is an "approved" grade for the Dmax.
My point is this: syns have an advantage ONLY when the OCI is pushed out far, so that their capabilities outperform a conventional lube as it degrades. But if you are only going to OCI at "normal" intervals, there is no "advantage" to using the syn because the capability of the dino oil is still well in control. There is PLENTY of proof that 10k mile OCIs with conventional oil is well within that capability of a dino lube. Your engine (which is one of the best wearing light duty diesels on the market) really doesn't care what lube you use, as long as it is a properly spec'd fluid.
It's not "wrong" to use T6 (or any other syn). But it's not a good decision to waste any product. Frankly, even dumping dino oil at 5k miles is a waste in a Dmax.
It would help you to figure out your overall use and maintenance plan, and then pick a lube that fits into those criteria.
* If you're going to do "normal" OCIs, I'd suggest using a conventional 10w-30 year round, and OCI when the OLM tells you to. You could do a compromise with the T5 here if yu choose.
* If you're in a position to drive a LOT of miles per year, then perhaps the advantage of syns can pay off with less downtime and such, and push your OCI out past the investment point. Do some UOAs for confirmation, and mangage your program well. It takes a committment to make this work, and many people fail here because they cannot keep their hands off the wrenches.
I would ask that you spend some time in the HDEO UOA section, and look over many of the Dmax UOAs, and you'll see the evidence for yourself.
