I have an 06 Duramax with 80K on it.
I have always gotten around 18 mph around town but it has recently fallen off to around 14. The change fuel filter message had come up so I changed it. I also changed the oil and put in a new air filter. I thought this would fix it but it didn't.
I went and got a bottle of Lucas Fuel Treatment and put it in with a full tank of fuel. My milage went back to 18 mpg with the first tankfull.
Has anyone else had results like this. I am sold on the stuff. I will be adding it to every 2nd or 3rd tank from now on.

I have an 02 lb7. I tried lucas but didnt see much of a change on anything. I now run powerservice in every other fill up. Not much of a gain in fuel economy but my injectors are quieter. As for fuel additives i look more for an additive with better lubrication than fuel economy. Mainly because the lb7 are known for injector failure and i also have 231000 miles on the original injectors.

Lucas is some if the best fuel additive I have used over the years. Power service is ok. Just never impressed me and yea I noticed the same thing where it lowers the mpg, especially on the 7.3 & 6.0 power strokes. If you want to know what the best stuff is I have ever seen & used is called Stanadyne. That stuff has saved my customers 1,000 of dollars and I have seen it work wonders and is good for the ulsd engines. Search e-bay for Stanadyne, I buy 3 bottles of there for 30 something with free shipping. For the ulsd engines I mix Lucas,Stanadyne, and regular ATF all togeather in a small bottle to add in my 02 Cummins and a few other machines and diesels I work on. If you mix that you take your own risk. But I have ran it mixed like that for years now. Are just use Stanadyne. You wont be dissapointed in that. Its good.

I have also heard great things about stanadyne. Just have not used it because i have not been able to find it anywhere local.

I have a 6/0 Power Stroke that used to get 17+ mpg all the time, its way down now to abour 12-13 with the lo sulphur fule, thats wher it dropped. I have a neighbor who keeps fuel,food,ammo etc for a emergency and had 15 gal of older fuel, I traded him new fule for it, my mileage went right back to 18!!! My friend rund 2-stroke oil in his fuel but I dont know if it helps (1 oz to 1 gal)