While I can't remember exactly at what point, but my old IS250 would lose power, and would regain it after a B12 chemtool to the tank treatment. Ran Kirkland/Chevron top tier, so that whole argument of gas is additized enough isn't true. I would always test the car on the same hill, speed set on cruise control. For the "after" I always made sure that the scenario would benefit the "before" outcomes, lower ambient temps, less warm up time, just so that the results would be biased in favor of the test run before the treatment. With that car, I knew when it was time because I drove that hill almost daily to get home. Today, I just run a couple bottles of whatever every 10k or so. If I suspect a problem, B12.