B service?

Ok, thank you for the information. I'm not up to speed on the newer engines.

 

I’m in the same boat, Same engine, but I run the PNW weekly, so I add mountains to an 87,000 lb load. That little 13L gets a workout. So we run about 40K between changes, and did the first overhead under the “severe” duty.
I figure it’s like fuel mileage. The savings going from 5 to 7 mpg is huge, but going from 7 to 8 is not near as beneficial. Going from 75K to 40 K basically adds a $400 oil change a year. Maybe not necessary, but I”ll bet I get most of that back when it comes to resale value.....