Probably the simplest cure to is a frequent change in fuel filters until the junk disappears that, of course, coupled with frequent use and more fresh fuel should work. I know that many marinas have the equipment to polish fuel which is nothing more than running it through a series of very large filters each finer than the previous and returning the fuel to the tank, sans additives. The process is supposed to clean the tank as well because of the high pressure of the fuel pumped back in stirs up the fluid and the process is continued until no debris is found. Caution here, polishing can also be interpreted by some as adding a jar of some kind of "snake oil" which in the final analysis may or may not work I can attest to the filter polishing, while I have not used the process on my bus, I have used it on boats. It takes longer than one may think, I do believe it took several hours to clean 200 gallons of fuel from my sailboat. I think I last filled that tank in the early 90's and it is still full....but that's a sailboat.

I do believe the the ultra low sulfur fuels have a lower cetane rating which may explain that issue, that can be overcome with a cetane boost. Alkyl nitrates (principally 2-ethyl hexyl nitrate ) and di-tert-butyl peroxide are used as additives to raise the cetane number. Look for it on the label.

Finally, jet fuel. Kerosene comes a bit higher on the cracking tower and with the exception of anti icing inhibitors I have never added anything to it. I would guess that I am personally responsible for burning at least a couple hundred thousand tons of that stuff and never a problem....however no jet sits on the ground very long.