So much has been said about oil additives that it makes the head spin. All I hear here is "that's why it's called snake oil" and "I used it and it worked OK." Reasonable enough opinions. But lubrication as a subject can't be ignored in the quest for good FE.
Thinking back to my first cars on to now with a modern vehicle (FI), additives and oil changes made more of an impact then. My air cooled VWs were rough and good oil in the right amount smoothed them out. Transmissions and shifting got easier, seemingly overnight.
Now modern oils are so good, those additives are felt less, and for me only careful tracking of FE and occasional teardowns (5.0 liter V8) keep me using additives. Tufoil has never failed to prove it's claim to being the "slipperiest substance in the world." They keep their customers for life because their products work. I was glad to see them mentioned here without undue derision.
Now that I have a baseline for the VX I recently bought, it's going in the crankcase and tranny for a FE test. Will report the results after a few hundred miles.