YOU were the one who threw out you were an engineering student like it somehow made you better or more knowledgable than everyone else. You were also the one who claimed that somehow spark plugs have changed your final drive ratio because you had "decreased RPM's at crusing speed"
Considering that speed and RPM are directly proportional in each gear that is downright impossible.
And you have no proof that you got increased fuel mileage because of the plugs. It likely has more to to with the difference in winter and summer blends of fuel, orr the fact that you changed from old worn plugs to new plugs.
Keep trying to make yourself seem smarter. We'll continue to laugh and point at how you spent $75 on a gimmick.