I've always ran something in all of my diesel trucks. So far on the 6.7 I've ran Power Service, Stanadyne, and Lucas products with less than stellar results. So after talking with the guys over at XDP they turned me on to their blend. I've been using this stuff with good results. So far (1k miles logged) my highway mpg is up 1mpg over none used. The truck idles even more quiet (yes that's possible). It's cheap, treats 500 gallons, and seems to really work. I haven't tried the winter blend obviously.
XDP Diesel Power Plus Fuel Additive
Figured I'd pass the word along.