I've been lokking into diesel fuel additives. Mostly I'm just looking for something that's a cleaner to use every once and a while to take care of the fuel system. I cam accross this Howe's Meaner Power Kleaner:
Howes Lubricator
Here's the catch: they say they gaurantee a 5% improvement in mileage. Now, I'm skeptical of course, but Howe's is a name that's been around since the 1920's. They claim they're the #1 one seller in truck stops. But 5% gaurenteed from a fuel additive! I can understand an "up to 5%" claim, but "5% gauranteed" is a different story.
It seems to be getting some good "reviews" on some of the other forums as well:
HOWES Meaner Power Kleaner is by far the BEST!!! - Dodge Diesel - Diesel Truck Resource Forums
I'm skeptical, but I'm thinking it might be worth a try.