Increasing the combustion pressure and temperature I think is the primary feature of running hard. It seems to be benificial in a lot of cases. The sensation of the car having a burp or whatever is interesting as well. I wonder if that might be carbon igniting or something simular. Might even be just cleaning out the exhaust for all I know. The pressure is high as well as the temperature is increased. That would upset the applecart for a moment perhaps. It is caused by something. Have always visulised the essential normal cheap tuneup as the really cheap one unless you have paid to have the injectors checked for example. A normal tune up is usually just time. Plus you get quicker at it with experience. The highway thing is perjhaps just icing on the cake as the car will not run it's best unless the other things are checked. It is always nice to hear of an engine running very well. Hopefully your fuel milage will be better now as well. Thats if you can keep your foot out of it with the increased performance.