Sea Foam
I have used it a few times with friends on various vehicles. I've used it personally added into the fuel tank only, with great results. I've used it in all of my quads to help keep the carburetors clean. All of the vehicles we did it to were a lot more responsive, they were all over 90k miles as well. Shortly after the 350Z developed a nasty tap throughout the RPM range! It hasn't been fixed yet, and we don't know if the Seafoam caused it. I have seen a few other similar situations online. Again, not sure if the Seafoam caused it, but it was awfully coincidental.
i've loved it on my other cars, both in the tank and through the intake. was fantastic on older cars as well. I'm not sure if i'd put it through a DI engine like the ecoboost either in the intake or gas tank, but for standard injection i'd go for it.

