Heck! I just can't win! The truck runs a bit better with the tone ring advanced but mileage is a down a bit. My last tank before the mod was exactly 16mpg and this tank after the mod was back down to 15.1 mpg.. My normal mileage is between 15 and 15.5 mpg. I'm not sure why the last tank was up to 16 but I did put some Power Service in that tank. Maybe I'll try running a whole week without the Quad box on but that's hard to do once you've run the box. I know the mileage will be better without the box because for the first couple days I ran the truck stock and the overhead, which is pretty accurate with no box, was showing 17mpg. After the first couple days I put the box on the 60hp setting since that's where I usually drive. Oh well.....

 

Just a dumb thought but have they maybe started with winter diesel in your area around the time of the last fillup?

 

I thought of that but I doubt it since it hasn't even been cold here at all yet. We're still wearing shorts....
I know it wasn't a heavy foot because I've been driving very passively trying to get the best mileage...