The reduced chamber size seems to be the biggest impact, not the build-up on the valves imho. BTW, you got yours really clean...my tongue wasn't long enough to get in thereIt seems like the 3.5 ecoboost fairs better than many other DI engines I have seen posted online with even less mileage. I feel like mine is idling smoother since cleaning but I replaced my spark plugs at the same time.
