It would be hard to say.....without knowing for sure you have a problem. Do you have a FF that reads speed? If so, you could get a WOT speed early in the day, as well as later on. I know sometimes my mind does funny things.....it sounds like you're "problem" is so slight, you're really not even sure you have a problem.
I'd look under the cover for gas/oil stains, and give it a shot of SeaFoam & as long as everything sounded good, and you don't have something noticeable, I wouldn't worry about it.
I'm assuming it's pumping water good? May want to replace your impeller sometime, just to know it's been done & is good.
ST