New Duramax Owner

I recommend two main items outside of following the OEM maintenance schedule:
1) Consider adding a catch can. I think the Mann Pro-Vent is the best one easily.
2) Take note that the diesel supplement started calling for adding a fuel conditioner in the last couple model years. I assume this change was due to some painful injector warranty for GM and so I would heed the suggestion. Of course GM says to use only AC Delco conditioner, but I suggest using whatever you like so long as it meets the other critical items GM lists - No alcohols, no organo-metallic, and no water emulsifiers (de-emulsifiers are fine). There's a bunch of great choices. I use Opti-Lube XL.

If your more of a tinkerer, some folks here have added a 2-micron secondary fuel filter from Racor but this isn't necessary and we have no evidence it helps.

You can otherwise peruse threads on oil selection and stuff, but there it's starts being opinions like a**holes, everyone has one. Most likely any Dexos2 certified oil is going to be a good selection. I think that's about it, the engine should give good service and is a pleasure to use when towing the kinds of loads that the Colorado was designed to handle.

If doing only one thing with longevity and reliability in mind, it is use a good lube and injector cleaner additive with each and every fill up with out fail if not running biodiesel. Biodiesel inherently has lubricating qualities in it. Modern low sulfur diesel fuel is "dry" as the de-sulfering process removes a lot of diesel's inherent lubrication qualities along with the sulfur.

The fuel sellers are supposed to include additives to reach America's (too low a bar in my opinion for sensitive modern diesel fuel systems) fuel lubricity specification, but those additives cost money and fuel sellers are in the business to make money on a slim margin product. Given all that, it is smart to make sure yourself that the fuel will not wear out/tear up the sensitive injectors and high pressure fuel pump, as a "failed injector" often burns a hole in it's cylinder's piston, which is a pain in the ass to say the least.

There are lots of "tweaks" that are great, but I think the fuel lube additive is mandatory for everybody. Do that and I think these engines can and should run a long time. The basic design has been around for years, and it is a low revving, low stress jolly little diesel

Speaking of revs, do not rev these things unnecessarily. Tow/haul mode is clumsy AF, and can really zing the revs up there past 4K on downhill engine braking scenarios. I don't do that to mine, brake pads and rotors, if it comes to it, are simple to replace and cheaper than a stressed/damaged engine. There are ways to get Tow/Haul to do your bidding without revving the nuts off the engine, but this post is already getting long!