Forgot to mention, this was at my Ford dealership! It wasn't at some independent mechanic.I would find a new mechanic, quickly. Techron does very little, and you can add a quart of fuel cleaner once a year that does a better job at a lot less price. I put 350,000 miles on my Dodge Neon, and now 113,000+ miles on my Focus with probably 95% Costco gas. Never ANY problem with the injectors and fuel system. I've used Chevron several times to test it... no difference in MPG between Costco & Chevron. Now, Arco is a different story. I've never put it in my Focus, and never will. With my Neon, the Arco MPG was lower, and the one time I climbed a 7% grade with it, there was a little roughness in the engine and a loss of 2-3 MPH. Maybe it's become better in the 10 years or so I've stayed away from it.
We used to use Arco way back in the day and definitely had loss of MPG. I can't comment on engine power, but there was a definite reduction in MPG. This was also about 7-8 years ago.