I've used Blackstone for many years on all of the various diesel rigs I have owned. I found that I could routinely go 10,000 miles between oil changes using regular 15w40 with plenty of safety margin. In fact, I could just change the filter at 10,000 miles and add 2 qts for what was lost in changing the filter and easily go another 5,000 miles with plenty of safety margin (adequate additives left with minimum particulates and fuel).
I routinely got 200,000 plus miles out of all those motors with zero failures. The ones I know of are still running fine without any major repairs.
Everyone has their own opinions and if changing your oil every 6 months or 5,000 mile is what makes you comfortable, then that is what is right for you. But, if you use the oil test reports on a regular basis you will find you can go much farther between changes with complete safety, especially when you're using the expensive synthetic stuff.
Randy Rosetta KDØKWX TLCA #19351 NOW 2015 Rubicon Hard Rock & (2) 1970 Boss 302 Mustang's THEN 69 FJ40 Buggy "Meanie", Mini-truck "Gecko" & 74 FJ40 "Blue Mule"