Good Day!
"Did your mileage go back up when you stopped using it?" Nope. I haven't looked closely, but it appears a general downward trend simply continued right through when I used Performance Formula & after I ran out of it. (I'm suspecting worn timing chain causing retarded injection timing, & old injectors; I'll bump the timing a little when I get time, the injectors, well...)
Blessings!(signature in previous post)