Herk, I'm thinking your gona need more than a gal. I use DK grey bottle in my 03 7.3 Ford every top off. I think (cant remember) it calsl for about 8oz for my 38 gal tank. I'm not that exact on the quantity I add but havent had any injector issues, yet. I don't have a base line of before/after results, I just use it. I don't believe it to be snake oil.
Matt & Kathie
2017 Grey Wolf 27RR