Obviously a controversial subject; especially if you suggest brand names. As an oil man for 20 years - the following might be helpful.
A few points- 1-Using a top quality engine oil is the cheapest insurance you can have. If it protects that one time things get too hot, etc. it's worth it's weight in cummins engines. 2- Use an oil rated for Diesel engines, ie. CG-4 or the newest rating (lower soot deposits) CI-4. 3- There are many misconceptions about synthetic engine oils. The truth is there are only 2 advantages to using synthetics (but their biggies). Synthetics have more thermal stability (work better if they get over 200 degreesF. ) and they last longer.
Best of the best synthetics are (in my humble opinion) Amsoil, Royal Purple and Synergyn Racing Oil and Devac I, if you can find it. All these are excellent and have enough additives to last as long as the oil itself. That being said, there are two ways to skin this cat! You can go with the cheapest oil you can find (must be at least CG-4 rated) and I would recommend changing oil & filter @ 3,000 miles if towing and 5,000 miles if not. This will work, as long as no problems cause oil to exceed 200-250 degrees F.
The advantages of higher quality oils mentioned above are 4: 1-Extended oil Changes; 7,500 miles if towing and 10,000 if not. 2- Protection if high temp occur. 3- Better protection for turbos, 4-Ability for the adventurous to go with a 5w-30 wt oil and get better cooling, due to more rapid flow and better mileage due to less drag. I picked up 1 mpg with Synergyn's 3-30 wt Racing Oil, switching from 15w-40. You must have highest quality oils to maintain protection when going to one of the 30 wts.
Testing and Oil analysis I have done for customers has shown me the better non synthetics diesel oils (in my area) are Delvac 1300, Chevron Delo 400 and Shells Rotella T. But at 7500 to 10,000 mile oil changes, the top synthetic oils are cost effective and offer much better protection, especially for turbo chargers.
Hope this helps you figure what you want to do?
Rowland