There's 2 reasons diesel costs as much as it does: 1, consumer demand. 2, the refining process and additives are more advanced than fuels of yesterday.
Some say additives aren't necessary with today's fuels and some say they are.
Hoosier, I don't know the details of the Mack, but his engine is definitely not like our engines. Remember, our engines don't have injection or secondary pumps, which were the the main driving force behind additive study and development. I'M NOT SAYING OUR ENGINES DON'T BENEFIT FROM ADDITIVE USE THOUGH. Just giving you a short history lesson.
There's lots of tests on the 'net (some better than others). Here's an example of one:
Lubricity Additive Study Results - Diesel Place
On a particular Dodge site, the best additive for lubricity was found to be B05 (5% Biodiesel)
Getting back to your Mack driver, lots of "old school" truckers dumped in motor oil, tranny fluid, corn oil, etc. Not because these were tested, but because "Joe's doin it, and he's got a million miles"
It's also proven that additive makers are a good "bet" due to increased demand (https://origin-www.glgroup.com/News/...ves-10305.html
but is that influencing prices, quality, testing procedures? Who knows. And does that mean they're right? again, who knows.
One of the benefits additive mfgrs claim is increased fuel mileage. Some cases it's "true", and some cases it's not: Diesel additives fail to improve fuel efficiency - Product Library - World Fishing
For the record though, I believe I got 1-2 mpg better when using Stanadyne, but in reality that's hard to prove due to so many variables.
You probably wanted someone to say, "use brand X because it's the best", but bottom line is, while they have benefits, in MOST situations additives aren't NECESSARY. But in case you're wondering, I use Stanadyne, PowerService, Amsoil, and/or vegetable oil, depending on what's available