Ah, the great fuel additive debate. These can be nearly as good as what brand of oil is "the best". Some who have been here as long or longer than I have seen these many, many, many times. Hook'em can attest to that. As indicated, ULSD doesn't have the lubricity it once did (prior to 06 I believe. There was a study done 12 yrs ago now by Diesel Place that compared the fuel additives on the market at that time. Bio came in first, Opti-Lube XPD came in 2d, Stanadyne, FPPF and AMSOIL (now called injector clean) were all in the top 10 for lubricity. There hasn't been a large batch study that anyone can find since that time so most refer back to that list. Many will say and use 2-stroke oil for lubricity.
Last month, AMSOIL put out a new article about lubricity in different states and a high frequency reciprocating rig (HFRR) lubricity test. They were testing AMSOIL Saber Professional 2-Stroke oil along with Quicksilver TC-W3, Penzoil Outboard TC-W3 and AMSOIL Diesel Injector Clean. The Diesel Injector Clean had the lowest wear scar meaning it provided the most lubricity.
Here is a link to the report.
Personally, as many have, I have tested many on that old list to include Opti-Lube XPD, Stanadyne, FPPF, AMSOIL and several others over the years here. Based on better fuel economy, quicker starts, smoother idles, I have stuck with AMSOIL Diesel Injector Clean combined with their Cetane Booster, which btw is now available combined into a new product simply called
AMSOIL Injector Clean + Cetane Booster. We have always recommended regular use of fuel additives. Doing so is doing what you can to help protect these expensive trucks as best you can. Which one is "the best" that is mostly someone's opinion based on their use of product X. My recommendation is try several different ones and see which provides "the best" results for you.
If I can be of assistance with anything, please don't hesitate to ask.