oil choice for diesel

Delo or Rotella and Fleetguard filters.
Also, the FLeetguard Airfilter out-flows the others (Wix, Fram, etc) hands down.

It has been discussed to death....lol

I use 5-40 Rotella T6 synthetic with a nano borate additive. Your choice may be different. So long as the oil meets the API and manufacturers certifications for your engine, you are good to go. Just adhere to the OEM recommended change intervals.

I use the Delo 400 dino oil that's always on sale at Costco for $29 for 3 gallons. Meets all specifications. Synthetics have a benefit if you live in very cold weather. Doesn't get cold enough in So Cal.

Filters are Cummins/Fleetguard from Amazon.

Rotella T6 synthetic and Wix filters.
You can change filters and run the oil longer. Just add one quart of make up oil

I use Mobile Delvac 1300 in my 2001 Dodge Cummins. I tried Rotella TTT, but the numbers weren't as good as they were with Delvac according to Blackstone Labs, so I went back to Delvac and have lived happily ever after. I do change it every 5,000 miles or so, sometimes a little over, just depends. It's only about $12 per gallon so a little more frequent oil changes aren't that big of a deal. And usually a Wix filter, or Bosch, or Fleetguard.

I have used Chevron Delo 400 15W-40 in all my Cummins diesels over the years, both 12 valve and 24 valve, summer and winter. No problems to date.
My current truck has 409,000+ miles.
I use NAPA Gold oil and air filters (Wix)
I did find, a couple of years ago, that in the fall it pays to run the fuel tank well below half full, then fill with Winter Blend fuel. Near zero temps with summer fuel means you probably won't be going anywhere until it warms up!

Whatever is on sale Every 4s engine I own runs on sale priced Dino 15-40. Except the wet clutch bikes get Rotella T6. Well, and I have put the spec 0w40 in the new car for the first couple oil changes , but it’s not necessary, just my current preference.
Maint interval is more important than brand of oil.
06 Cummins will live a healthy life on pretty much anything that says 15-40 on the jug.

It doesn't get crazy cold or hot here and since the Cummins will happily go 500~1M miles on Dino, that's what I use. I tried syn for a few changes but saw no difference in mileage or anything else. Since I can't take advantage of it, it's just a waste for me to use syn.

Oil is like mouthwash, everyone has their favorite. I just go by the API cert and the manufacturers reccomendation on change intervals...